Chroma coding mode determination based on matrix-based intra prediction

ABSTRACT

Devices, systems and methods for digital video coding, which includes matrix-based intra prediction methods for video coding, are described. In a representative aspect, a method for video processing includes performing a first determination that a luma video block of a video is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the luma video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, performing, based on the first determination, a second determination about a chroma intra mode to be used for a chroma video block associated with the luma video block, and performing, based on the second determination, a conversion between the chroma video block and a bitstream representation of the chroma video block.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application No. PCT/CN2020/084488, filed on Apr. 13, 2020, which claims the priority to and benefits of International Patent Application No. PCT/CN2019/082424, filed on Apr. 12, 2019. All the aforementioned patent applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to video coding techniques, devices and systems.

BACKGROUND

In spite of the advances in video compression, digital video still accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.

SUMMARY

Devices, systems and methods related to digital video coding, and specifically, matrix-based intra prediction methods for video coding are described. The described methods may be applied to both the existing video coding standards (e.g., High Efficiency Video Coding (HEVC)) and future video coding standards (e.g., Versatile Video Coding (VVC)) or codecs.

A first example video processing method includes generating, for a conversion between a current video block of a video and a coded representation of the current video block, a first most probable mode (MPM) list using a first procedure based on a rule; and performing the conversion between the current video block and the coded representation of the current video block using the first MPM list, where the conversion of the current video block uses a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where the rule specifies that the first procedure used for generation of the first MPM list is same as a second procedure used for generation of a second MPM list for conversion of other video blocks of the video that are coded using a non-MIP intra mode that is different from the MIP mode, and where at least a portion of the first MPM list is generated based on at least a portion of the second MPM list.

A second example video processing method includes generating, for a conversion between a current video block of a video and a coded representation of the current video block, a most probable mode (MPM) list based on a rule, where the rule is based on whether a neighboring video block of the current video block is coded with a matrix based intra prediction (MIP) mode in which a prediction block of the neighboring video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; and performing the conversion between the current video block and the coded representation of the current video block using the MPM list, where the conversion applies a non-MIP mode to the current video block, and where the non-MIP mode is different from the MIP mode.

A third example video processing method includes decoding a current video block of a video that is coded in a coded representation of the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; and updating a line buffer associated with the decoding without storing in the line buffer information indicating whether the current video block is coded using the MIP mode.

A fourth example video processing method includes performing a conversion between a current video block and a bitstream representation of the current video block, where the current video block is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where a flag is coded in the bitstream presentation using at most K contexts in an arithmetic coding or a decoding process, where the flag indicates whether the current video block is coded using the MIP mode, and where K is greater than or equal to zero.

A fifth example video processing method includes generating, for a conversion between a current video block of a video and a bitstream representation of the current video block, an intra prediction mode for the current video block coded with a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; determining a rule for storing information indicative of the intra prediction mode based on whether the current video block is coded with the MIP mode; and performing the conversion according to the rule, where the rule defines that a syntax element for the intra prediction mode is stored in the bitstream representation for the current video block, and where the rule defines that a mode index for the MIP mode for the current video block is not stored in the bitstream representation.

A sixth example video processing method includes performing a first determination that a luma video block of a video is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the luma video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; performing, based on the first determination, a second determination about a chroma intra mode to be used for a chroma video block associated with the luma video block; and performing, based on the second determination, a conversion between the chroma video block and a bitstream representation of the chroma video block.

A seventh example video processing method includes performing a conversion between a current video block of a video and a coded representation of the current video block, where the conversion is based on a determination whether to code the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation.

An eight example video processing method includes determining, for encoding a current video block of a video into a bitstream representation of the current video block, according to a rule whether to use a matrix based intra prediction (MIP) mode and a coding mode that is different from the MIP mode for encoding the current video block, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; and adding, based on the determining, an encoded representation of the current video block to the bitstream representation.

A ninth example video processing method includes determining that a current video block of a video is encoded in a bitstream representation using a matrix based intra prediction (MIP) mode and a coding mode that is different from the MIP mode, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; and generating a decoded representation of the current video block by parsing and decoding the bitstream representation.

A tenth example video processing method includes making a determination about an applicability of a loop filter to a reconstructed block of a current video block of a video in a conversion between the video and a coded representation of the current video block, where the current video block is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; and processing the current video block according to the determination.

An eleventh example video processing method includes determining, for encoding a current video block of a video into a bitstream representation of the current video block, a type of neighboring samples of the current video block to be used according to a rule; and adding, based on the determining, an encoded representation of the current video block to the bitstream representation, where the current video block is encoded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation.

A twelfth example video processing method includes determining that a current video block of a video is encoded in a bitstream representation using a matrix based intra prediction (MIP) mode and using a type of neighboring samples of the current video block according to a rule, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; and generating a decoded representation of the current video block by parsing and decoding the bitstream representation.

A thirteenth example video processing method includes performing a conversion between a current video block of a video and a bitstream representation of the current video block, where the conversion includes generating, by using a matrix based intra prediction (MIP) mode, a prediction block for the current video block by selecting and applying matrix multiplication using matrices of samples and/or by selecting and adding an offset using offset vectors for the current video block, where the samples are obtained from a row and column wise averaging of previously coded samples of the video, and where the selecting is based on reshaping information associated with applying a luma mapping with chroma scaling (LMCS) technique on a reference picture of the current video block.

A fourteenth example video processing method includes determining that a current video block is to be coded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; and performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block, where the performing the conversion is based on a rule of co-application of the MIP mode and another coding technique.

A fifteenth example video processing method includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode, where the performing the conversion using the MIP mode includes generating a prediction block by applying matrix multiplication using matrices of samples obtained from a row and column wise averaging of previously coded samples of the video, and where the matrices depend on a bit-depth of a sample.

A sixteenth example video processing method includes generating, for a current video block of a video, an intermediate prediction signal using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; generating, based on the intermediate prediction signal, a final prediction signal; and performing, based on the final prediction signal, a conversion between the current video block and a bitstream representation of the current video block.

A seventeenth example video processing method includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode, where the performing the conversion includes using an interpolation filter in an upsampling process for the MIP mode, where, in the MIP mode, a matrix multiplication is applied to a first set of samples obtained from a row and column wise averaging of previously coded samples of the video, and the interpolation filter is applied to a second set of samples obtained from the matrix multiplication, and where interpolation filter excludes a bilinear interpolation filter.

An eighteenth example video processing method includes performing a conversion between a current video block of a video and a bitstream representation of the current video block according to a rule, where the rule specifies a relationship between applicability of a matrix based intra prediction (MIP) mode or a transform mode during the conversion, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, and where the transform mode specifies use of a transform operation for the determining the prediction block for the current video block.

A nineteenth example video processing method includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where the performing the conversion includes deriving, according to a rule, boundary samples by applying a left bit shift operation or a right bit shift operation on a sum of at least one reference boundary sample, and where the rule determines whether to apply the left bit shift operation or the right bit shift operation.

A twentieth example video processing method includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where the prediction samples predSamples[xHor+dX][yHor] are determined according to following formula in the upsampling operation: predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor, and predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer, where offsetHor and offsetVer are integers, where upHor is a function of the current video block width and a pre-defined value based on the current video block size, where upVer is a function of the current video block height and the pre-defined value based on the current video block size; where dX is 1 . . . upHor−1, where dY is 1 . . . upVer−1, and where xHor are positions based on the upHor and yHor are positions based on the upVer.

A twenty-first example video processing method includes generating, for a conversion between a current video block of a video and a bitstream representation of the current video block, an intra prediction mode for the current video block coded with a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation; determining a rule for storing information indicative of the intra prediction mode based on whether the current video block is coded with the MIP mode; and performing the conversion according to the rule, where the rule defines that the bitstream representation excludes a storage of information indicative of the MIP mode associated with the current video block.

In yet another representative aspect, the disclosed technology may be used to provide a method for video processing. This exemplary method includes determining that a current video block is coded using an affine linear weighted intra prediction (ALWIP) mode, constructing, based on the determining, at least a portion of a most probable mode (MPM) list for the ALWIP mode based on an at least a portion of an MPM list for a non-ALWIP intra mode, and performing, based on the MPM list for the ALWIP mode, a conversion between the current video block and a bitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may be used to provide a method for video processing. This exemplary method includes determining that a luma component of a current video block is coded using an affine linear weighted intra prediction (ALWIP) mode, inferring, based on the determining, a chroma intra mode, and performing, based on the chroma intra mode, a conversion between the current video block and a bitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may be used to provide a method for video processing. This exemplary method includes determining that a current video block is coded using an affine linear weighted intra prediction (ALWIP) mode, and performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may be used to provide a method for video processing. This exemplary method includes determining that a current video block is coded using a coding mode different from an affine linear weighted intra prediction (ALWIP) mode, and performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block.

In yet another representative aspect, the above-described method is embodied in the form of processor-executable code and stored in a computer-readable program medium.

In yet another representative aspect, a device that is configured or operable to perform the above-described method is disclosed. The device may include a processor that is programmed to implement this method.

In yet another representative aspect, a video decoder apparatus may implement a method as described herein.

The above and other aspects and features of the disclosed technology are described in greater detail in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of 33 intra prediction directions.

FIG. 2 shows an example of 67 intra prediction modes.

FIG. 3 shows an example of locations of samples used for the derivation of the weights of the linear model.

FIG. 4 shows an example of four reference lines neighboring a prediction block.

FIG. 5A and FIG. 5B show examples of sub-partitions depending on block size.

FIG. 6 shows an example of ALWIP for 4×4 blocks.

FIG. 7 shows an example of ALWIP for 8×8 blocks.

FIG. 8 shows an example of ALWIP for 8×4 blocks.

FIG. 9 shows an example of ALWIP for 16×16 blocks.

FIG. 10 shows an example of neighboring blocks using in MPM list construction.

FIG. 11 shows a flowchart of an example method for matrix-based intra prediction, in accordance with the disclosed technology.

FIG. 12 shows a flowchart of another example method for matrix-based intra prediction, in accordance with the disclosed technology.

FIG. 13 shows a flowchart of yet another example method for matrix-based intra prediction, in accordance with the disclosed technology.

FIG. 14 shows a flowchart of yet another example method for matrix-based intra prediction, in accordance with the disclosed technology.

FIG. 15 is a block diagram of an example of a hardware platform for implementing a visual media decoding or a visual media encoding technique described in the present document.

FIG. 16 is a block diagram showing an example video processing system in which various techniques disclosed herein may be implemented.

FIG. 17 is a block diagram that illustrates an example video coding system that may utilize the techniques of this disclosure.

FIG. 18 is a block diagram illustrating an example of video encoder.

FIG. 19 is a block diagram illustrating an example of video decoder.

FIGS. 20-38 show example flowcharts of additional example methods for matrix-based intra prediction, in accordance with the disclosed technology.

DETAILED DESCRIPTION

Due to the increasing demand of higher resolution video, video coding methods and techniques are ubiquitous in modern technology. Video codecs typically include an electronic circuit or software that compresses or decompresses digital video and are continually being improved to provide higher coding efficiency. A video codec converts uncompressed video to a compressed format or vice versa. There are complex relationships between the video quality, the amount of data used to represent the video (determined by the bit rate), the complexity of the encoding and decoding algorithms, sensitivity to data losses and errors, ease of editing, random access, and end-to-end delay (latency). The compressed format usually conforms to a standard video compression specification, e.g., the High Efficiency Video Coding (HEVC) standard (also known as H.265 or MPEG-H Part 2), the Versatile Video Coding (VVC) standard to be finalized, or other current and/or future video coding standards.

Embodiments of the disclosed technology may be applied to existing video coding standards (e.g., HEVC, H.265) and future standards to improve runtime performance. Section headings are used in the present document to improve readability of the description and do not in any way limit the discussion or the embodiments (and/or implementations) to the respective sections only.

1 A Brief Review on HEVC 1.1 Intra Prediction in HEVC/H.265

Intra prediction involves producing samples for a given TB (transform block) using samples previously reconstructed in the considered color channel. The intra prediction mode is separately signaled for the luma and chroma channels, with the chroma channel intra prediction mode optionally dependent on the luma channel intra prediction mode via the ‘DM_CHROMA’ mode. Although the intra prediction mode is signaled at the PB (prediction block) level, the intra prediction process is applied at the TB level, in accordance with the residual quad-tree hierarchy for the CU, thereby allowing the coding of one TB to have an effect on the coding of the next TB within the CU, and therefore reducing the distance to the samples used as reference values.

HEVC includes 35 intra prediction modes—a DC mode, a planar mode and 33 directional, or ‘angular’ intra prediction modes. The 33 angular intra prediction modes are illustrated in FIG. 1.

For PBs associated with chroma color channels, the intra prediction mode is specified as either planar, DC, horizontal, vertical, ‘DM_CHROMA’ mode or sometimes diagonal mode ‘34’.

Note for chroma formats 4:2:2 and 4:2:0, the chroma PB may overlap two or four (respectively) luma PBs; in this case the luma direction for DM_CHROMA is taken from the top left of these luma PBs.

The DM_CHROMA mode indicates that the intra prediction mode of the luma color channel PB is applied to the chroma color channel PBs. Since this is relatively common, the most-probable-mode coding scheme of the intra_chroma_pred_mode is biased in favor of this mode being selected.

2 Examples of Intra Prediction in VVC

2.1 Intra Mode Coding with 67 Intra Prediction Modes

To capture the arbitrary edge directions presented in natural video, the number of directional intra modes is extended from 33, as used in HEVC, to 65. The additional directional modes are depicted as red dotted arrows in FIG. 2, and the planar and DC modes remain the same. These denser directional intra prediction modes apply for all block sizes and for both luma and chroma intra predictions.

2.2 Examples of the Cross-Component Linear Model (CCLM)

In some embodiments, and to reduce the cross-component redundancy, a cross-component linear model (CCLM) prediction mode (also referred to as LM), is used in the JEM, for which the chroma samples are predicted based on the reconstructed luma samples of the same CU by using a linear model as follows:

pred _(c)(i,j)=β·rec _(L)′(i,j)+β  (1)

Here, pred_(c) (i, j) represents the predicted chroma samples in a CU and rec_(L)′(i,j) represents the downsampled reconstructed luma samples of the same CU. Linear model parameter α and β are derived from the relation between luma values and chroma values from two samples, which are luma sample with minimum sample value and with maximum sample inside the set of downsampled neighboring luma samples, and their corresponding chroma samples. FIG. 3 shows an example of the location of the left and above samples and the sample of the current block involved in the CCLM mode.

This parameter computation is performed as part of the decoding process, and is not just as an encoder search operation. As a result, no syntax is used to convey the α and β values to the decoder.

For chroma intra mode coding, a total of 8 intra modes are allowed for chroma intra mode coding. Those modes include five traditional intra modes and three cross-component linear model modes (CCLM, LM_A, and LM_L). Chroma mode coding directly depends on the intra prediction mode of the corresponding luma block. Since separate block partitioning structure for luma and chroma components is enabled in I slices, one chroma block may correspond to multiple luma blocks. Therefore, for Chroma DM mode, the intra prediction mode of the corresponding luma block covering the center position of the current chroma block is directly inherited.

2.3 Multiple Reference Line (MRL) Intra Prediction

Multiple reference line (MRL) intra prediction uses more reference lines for intra prediction. In FIG. 4, an example of 4 reference lines is depicted, where the samples of segments A and F are not fetched from reconstructed neighboring samples but padded with the closest samples from Segment B and E, respectively. HEVC intra-picture prediction uses the nearest reference line (i.e., reference line 0). In MRL, 2 additional lines (reference line 1 and reference line 3) are used. The index of selected reference line (mrl_idx) is signalled and used to generate intra predictor. For reference line idx, which is greater than 0, only include additional reference line modes in MPM list and only signal mpm index without remaining mode.

2.4 Intra Sub-Partitions (ISP)

The Intra Sub-Partitions (ISP) tool divides luma intra-predicted blocks vertically or horizontally into 2 or 4 sub-partitions depending on the block size. For example, minimum block size for ISP is 4×8 (or 8×4). If block size is greater than 4×8 (or 8×4) then the corresponding block is divided by 4 sub-partitions. FIG. 5 shows examples of the two possibilities. All sub-partitions fulfill the condition of having at least 16 samples.

For each sub-partition, reconstructed samples are obtained by adding the residual signal to the prediction signal. Here, a residual signal is generated by the processes such as entropy decoding, inverse quantization and inverse transform. Therefore, the reconstructed sample values of each sub-partition are available to generate the prediction of the next sub-partition, and each sub-partition is processed repeatedly. In addition, the first sub-partition to be processed is the one containing the top-left sample of the CU and then continuing downwards (horizontal split) or rightwards (vertical split). As a result, reference samples used to generate the sub-partitions prediction signals are only located at the left and above sides of the lines. All sub-partitions share the same intra mode.

2.5 Affine Linear Weighted Intra Prediction (ALWIP or Matrix-Based Intra Prediction)

Affine linear weighted intra prediction (ALWIP, a.k.a. Matrix based intra prediction (MIP)) is proposed in JVET-N0217.

In JVET-N0217, two tests are conducted. In test 1, ALWIP is designed with a memory restriction of 8K bytes and at most 4 multiplications per sample. Test 2 is similar to test 1, but further simplifies the design in terms of memory requirement and model architecture.

-   -   Single set of matrices and offset vectors for all block shapes.     -   Reduction of number of modes to 19 for all block shapes.     -   Reduction of memory requirement to 576010-bit values, that is         7.20 Kilobyte.     -   Linear interpolation of predicted samples is carried out in a         single step per direction replacing iterative interpolation as         in the first test.

2.5.1 Test 1 of JVET-N0217

For predicting the samples of a rectangular block of width W and height H, affine linear weighted intra prediction (ALWIP) takes one line of H reconstructed neighboring boundary samples left of the block and one line of W reconstructed neighboring boundary samples above the block as input. If the reconstructed samples are unavailable, they are generated as it is done in the conventional intra prediction.

The generation of the prediction signal is based on the following three steps:

Out of the boundary samples, four samples in the case of W=H=4 and eight samples in all other cases are extracted by averaging.

A matrix vector multiplication, followed by addition of an offset, is carried out with the averaged samples as an input. The result is a reduced prediction signal on a subsampled set of samples in the original block.

The prediction signal at the remaining positions is generated from the prediction signal on the subsampled set by linear interpolation which is a single step linear interpolation in each direction.

The matrices and offset vectors needed to generate the prediction signal are taken from three sets S₀, S₁, S₂ of matrices. The set S₀ consists of 18 matrices A₀ ^(i), i ∈ {0, . . . , 17} each of which has 16 rows and 4 columns and 18 offset vectors b₀ ^(i), i ∈{0, . . . , 17} each of size 16. Matrices and offset vectors of that set are used for blocks of size 4×4. The set S₁ consists of 10 matrices A₁ ^(i), i ∈{0, . . . , 9}, each of which has 16 rows and 8 columns and 10 offset vectors bf, i ∈{0, . . . , 9} each of size 16. Matrices and offset vectors of that set are used for blocks of sizes 4×8, 8×4 and 8×8. Finally, the set S₂ consists of 6 matrices A₂ ^(i), i ∈{0, . . . , 5}, each of which has 64 rows and 8 columns and of 6 offset vectors b₂ ^(i), i ∈{0, . . . , 5} of size 64. Matrices and offset vectors of that set or parts of these matrices and offset vectors are used for all other block-shapes.

The total number of multiplications needed in the computation of the matrix vector product is always smaller than or equal to 4×W×H. In other words, at most four multiplications per sample are required for the ALWIP modes.

2.5.2 Averaging of the Boundary

In a first step, the input boundaries bdry^(top) and bdry^(left) are reduced to smaller boundaries bdry_(red) ^(top) and bdry_(red) ^(left). Here, bdry_(red) ^(top) and bdry_(red) ^(left) both consists of 2 samples in the case of a 4×4-block and both consist of 4 samples in all other cases.

In the case of a 4×4-block, for 0≤i<2, one defines

${bdr{y_{red}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{1}{bdr{y^{top}\left\lbrack {{i \cdot 2} + j} \right\rbrack}}} \right) + 1} \right) ⪢ 1}$

and defines bdry_(red) ^(left) analogously.

Otherwise, if the block-width W is given as W=4·2^(k), for 0≤i<4, one defines

${{bdr}{y_{red}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{2^{k} - 1}{bdr{y^{top}\left\lbrack {{i \cdot 2^{k}} + j} \right\rbrack}}} \right) + \left( {1 ⪡ \left( {k - 1} \right)} \right)} \right) ⪢ k}$

and defines bdry_(red) ^(left) analogously.

The two reduced boundaries bdry_(red) ^(top) and bdry_(red) ^(left) are concatenated to a reduced boundary vector bdry_(red) which is thus of size four for blocks of shape 4×4 and of size eight for blocks of all other shapes. If mode refers to the ALWIP-mode, this concatenation is defined as follows:

${bdry_{red}} = \left\{ {\begin{matrix} \left\lbrack {{{bdr}y_{red}^{top}}\ ,\ {{bdr}y_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} < 18}}} \\ \left\lbrack {{bdry_{red}^{left}},\ {{bdr}y_{red}^{top}}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 18}}} \\ \left\lbrack {{{bdr}y_{red}^{top}}\ ,\ {{bdr}y_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} < 10}} \\ \left\lbrack {{{bdr}y_{red}^{left}},\ {{bdr}y_{red}^{top}}} \right\rbrack & {{{for}{\mspace{11mu}\ }{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 10}} \\ \left\lbrack {{{bdr}y_{red}^{top}}\ ,\ {{bdr}y_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} < 6} \\ \left\lbrack {{{bdr}y_{red}^{left}},\ {{bdr}y_{red}^{top}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 6} \end{matrix}.} \right.$

Finally, for the interpolation of the subsampled prediction signal, on large blocks a second version of the averaged boundary is needed. Namely, if min(W, H)>8 and W≥H, one writes W=8*2^(l), and, for 0≤i<8, defines

${{bdr}{y_{redII}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{2^{l} - 1}{bdr{y^{top}\left\lbrack {{i \cdot 2^{l}} + j} \right\rbrack}}} \right) + \left( {1 ⪡ \left( {l - 1} \right)} \right)} \right) ⪢ {l.}}$

If min(W, H)>8 and H>W, one defines bdry_(redII) ^(left) analogously.

2.5.3 Generation of the Reduced Prediction Signal by Matrix Vector Multiplication

Out of the reduced input vector bdry_(red) one generates a reduced prediction signal pred_(red). The latter signal is a signal on the downsampled block of width W_(red) and height H_(red). Here, W_(red) and H_(red) are defined as:

$W_{red} = \left\{ {{\begin{matrix} 4 & {{{{for}\mspace{14mu}\max\left( {W,H} \right)} \leq 8}\mspace{14mu}} \\ {\min\left( {W,8} \right)} & {{{for}\mspace{14mu}\max\left( {W,H} \right)} > 8} \end{matrix}H_{red}} = \left\{ \begin{matrix} 4 & {{{{for}\mspace{14mu}\max\left( {W,H} \right)} \leq 8}\mspace{14mu}} \\ {\min\left( {H,8} \right)} & {{{for}\mspace{14mu}\max\left( {W,H} \right)} > 8} \end{matrix} \right.} \right.$

The reduced prediction signal pred_(red) is computed by calculating a matrix vector product and adding an offset:

pred_(red) =A·bdry_(red) +b

Here, A is a matrix that has W_(red)·H_(red) rows and 4 columns if W=H=4 and 8 columns in all other cases. b is a vector of size W_(red)·H_(red).

The matrix A and the vector b are taken from one of the sets S₀, S₁, S₂ as follows. One defines an index idx=idx(W, H) as follows:

${id{x\left( {W,H} \right)}} = \left\{ {{\begin{matrix} 0 & {{{for}\mspace{14mu} W} = {H = 4}} \\ 1 & {{{for}\mspace{14mu}\max\left( {W,H} \right)} = 8} \\ 2 & {{{for}\mspace{14mu}\max\left( {W,H} \right)} > 8} \end{matrix}.m} = \left\{ {\begin{matrix} {mode} & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} < 18}}} \\ {{mode} - 17} & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 18}}} \\ {mode} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} < 10}} \\ {{mode} - 9} & {{{for}\mspace{14mu}\max\;\left( {W,H} \right)} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 10}} \\ {mode} & {{{for}{\;\mspace{9mu}}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} < 6} \\ {{mode} - 5} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 6} \end{matrix}.} \right.} \right.$

Moreover, one puts m as follows:

Then, if idx≤1 or idx=2 and min(W, H)>4, one puts A=A_(idx) ^(m) and b=b_(idx) ^(m). In the case that idx=2 and min(W, H)=4, one lets A be the matrix that arises by leaving out every row of A_(idx) ^(m) that, in the case W=4, corresponds to an odd x-coordinate in the downsampled block, or, in the case H=4, corresponds to an odd y-coordinate in the downsampled block.

Finally, the reduced prediction signal is replaced by its transpose in the following cases:

-   -   W=H=4 and mode≥18     -   max(W, H)=8 and mode≥10     -   max(W, H)>8 and mode≥6

The number of multiplications required for calculation of pred_(red) is 4 in the case of W=H=4 since in this case A has 4 columns and 16 rows. In all other cases, A has 8 columns and W_(red)·H_(red) rows and one immediately verifies that in these cases 8·W_(red)·H_(red)≤4·W·H multiplications are required, i.e. also in these cases, at most 4 multiplications per sample are needed to compute pred_(red).

2.5.4 Illustration of the Entire ALWIP Process

The entire process of averaging, matrix vector multiplication and linear interpolation is illustrated for different shapes in FIGS. 6-9. Note, that the remaining shapes are treated as in one of the depicted cases.

1. Given a 4×4 block, ALWIP takes two averages along each axis of the boundary. The resulting four input samples enter the matrix vector multiplication. The matrices are taken from the set S₀. After adding an offset, this yields the 16 final prediction samples. Linear interpolation is not necessary for generating the prediction signal. Thus, a total of (4·16)/(4·4)=4 multiplications per sample are performed.

2. Given an 8×8 block, ALWIP takes four averages along each axis of the boundary. The resulting eight input samples enter the matrix vector multiplication. The matrices are taken from the set S₁. This yields 16 samples on the odd positions of the prediction block. Thus, a total of (8·16)/(8·8)=2 multiplications per sample are performed. After adding an offset, these samples are interpolated vertically by using the reduced top boundary. Horizontal interpolation follows by using the original left boundary.

3. Given an 8×4 block, ALWIP takes four averages along the horizontal axis of the boundary and the four original boundary values on the left boundary. The resulting eight input samples enter the matrix vector multiplication. The matrices are taken from the set S_(i). This yields 16 samples on the odd horizontal and each vertical positions of the prediction block. Thus, a total of (8·16)/(8·4)=4 multiplications per sample are performed. After adding an offset, these samples are interpolated horizontally by using the original left boundary.

4. Given a 16×16 block, ALWIP takes four averages along each axis of the boundary. The resulting eight input samples enter the matrix vector multiplication. The matrices are taken from the set S₂. This yields 64 samples on the odd positions of the prediction block. Thus, a total of (8·64)/(16·16)=2 multiplications per sample are performed. After adding an offset, these samples are interpolated vertically by using eight averages of the top boundary. Horizontal interpolation follows by using the original left boundary. The interpolation process, in this case, does not add any multiplications. Therefore, totally, two multiplications per sample are required to calculate ALWIP prediction.

For larger shapes, the procedure is essentially the same and it is easy to check that the number of multiplications per sample is less than four.

For W×8 blocks with W>8, only horizontal interpolation is necessary as the samples are given at the odd horizontal and each vertical positions.

Finally, for W×4 blocks with W>8, let A_kbe the matrix that arises by leaving out every row that corresponds to an odd entry along the horizontal axis of the downsampled block. Thus, the output size is 32 and again, only horizontal interpolation remains to be performed.

The transposed cases are treated accordingly.

2.5.5 Single Step Linear Interpolation

For a W×H block with max(W, H)≥8, the prediction signal arises from the reduced prediction signal pred_(red) on W_(red)×H_(red) by linear interpolation. Depending on the block shape, linear interpolation is done in vertical, horizontal or both directions. If linear interpolation is to be applied in both directions, it is first applied in horizontal direction if W<H and it is first applied in vertical direction, else.

Consider without loss of generality a W×H block with max(W, H)≥8 and W≥H. Then, the one-dimensional linear interpolation is performed as follows. Without loss of generality, it suffices to describe linear interpolation in vertical direction. First, the reduced prediction signal is extended to the top by the boundary signal. Define the vertical upsampling factor U_(ver)=H/H_(red) and write U_(ver)=2^(u) ^(ver) >1. Then, define the extended reduced prediction signal by

${pre{{d_{red}\lbrack x\rbrack}\left\lbrack {- 1} \right\rbrack}} = \left\{ {\begin{matrix} {{{bdr}{y_{red}^{top}\lbrack x\rbrack}}\mspace{11mu}} & {{{for}\mspace{14mu} W} = 8} \\ {{{bdr}{y_{redII}^{top}\lbrack x\rbrack}}\mspace{11mu}} & {{{for}\mspace{14mu} W} > 8} \end{matrix}.} \right.$

Then, from this extended reduced prediction signal, the vertically linear interpolated prediction signal is generated by

${pre{{d_{red}^{{ups},{ver}}\lbrack x\rbrack}\left\lbrack {{U_{ver} \cdot y} + k} \right\rbrack}} = {\left( {{\left( {U_{ver} - k - 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\left\lbrack {y - 1} \right\rbrack}} + {\left( {k + 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\lbrack y\rbrack}} + \frac{U_{ver}}{2}} \right) ⪢ u_{ver}}$   for  0 ≤ x < W_(red), 0 ≤ y < H_(red)  and  0 ≤ k < U_(ver).

2.5.6 Signalization of the Proposed Intra Prediction Modes

For each Coding Unit (CU) in intra mode, a flag indicating if an ALWIP mode is to be applied on the corresponding Prediction Unit (PU) or not is sent in the bitstream. The signalization of the latter index is harmonized with MRL in the same way as in JVET-M0043. If an ALWIP mode is to be applied, the index predmode of the ALWIP mode is signaled using a MPM-list with 3 MPMS.

Here, the derivation of the MPMs is performed using the intra-modes of the above and the left PU as follows. There are three fixed tables map_angular_to_alwip_(idx), idx ∈{0,1,2} that assign to each conventional intra prediction mode predmode_(Angular) an ALWIP mode

predmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an index

idx(PU)=idx(W,H)∈{0,1,2}

that indicates from which of the three sets the ALWIP-parameters are to be taken as in Section 2.5.3.

If the above Prediction Unit PU_(above) is available, belongs to the same CTU as the current PU and is in intra mode, if idx(PU)=idx(PU_(above)) and if ALWIP is applied on PU_(above) with ALWIP-mode predmode_(ALWIP) ^(above), one puts

mode_(ALWIP)^(above) = predmode_(ALWIP)^(above).

If the above PU is available, belongs to the same CTU as the current PU and is in intra mode and if a conventional intra prediction mode predmode_(Angular) ^(above) is applied on the above PU, one puts

mode_(ALWIP)^(above) = map_angular_to_alwip_(idx(PU_(above)))[predmode_(Angular)^(above)].

In all other cases, one puts

mode_(ALWIP)^(above) = −1,

which means that this mode is unavailable. In the same way but without the restriction that the left PU needs to belong to the same CTU as the current PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx ∈{0,1,2} are provided, each of which contains three distinct ALWIP modes. Out of the default list list_(idx(pu)) and the modes mode_(ALWIP) ^(above) and mode_(ALWIP) ^(left), one constructs three distinct MPMs by substituting −1 by default values as well as eliminating repetitions.

The left neighboring block and above neighboring block used in the ALWIP MPM list construction is A1 and B1 as shown in FIG. 10.

2.5.7 Adapted MPM-List Derivation for Conventional Luma and Chroma Intra-Prediction Modes

The proposed ALWIP-modes are harmonized with the MPM-based coding of the conventional intra-prediction modes as follows. The luma and chroma MPM-list derivation processes for the conventional intra-prediction modes uses fixed tables map_alwip_to_angular_(idx), idx ∈{0,1,2}, mapping an ALWIP-mode predmode_(ALWIP) on a given PU to one of the conventional intra-prediction modes

predmode_(Angular)=map_alwip_to_angular_(idx(PU))[predmode_(ALWIP)]

For the luma MPM-list derivation, whenever a neighboring luma block is encountered which uses an ALWIP-mode predmode_(ALWIP), this block is treated as if it was using the conventional intra-prediction mode predmode_(Angular). For the chroma MPM-list derivation, whenever the current luma block uses an LWIP-mode, the same mapping is used to translate the ALWIP-mode to a conventional intra prediction mode.

2.5.8 Corresponding Modified Working Draft

In some embodiments, as described in this section, portions related to intra_lwip_flag, intra_lwip_mpm_flag, intra_lwip_mpm_idx and intra_lwip_mpm_remainder have been added to the working draft based on embodiments of the disclosed technology.

In some embodiments, as described in this section, the <begin> and <end> tags are used to denote additions and modifications to the working draft based on embodiments of the disclosed technology.

Syntax Tables Coding Unit Syntax

Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {  if( tile_group_type !=I | | sps_ibc_enabled_flag ) {   if( treeType != DUAL_TREE_CHROMA )    cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 && tile_group_type != I )    pred_mode_flag ae(v)   if( ( ( tile_group_type = = I && cu_skip_flag[ x0 ][ y0 ] = =0 ) | |    ( tile_group_type != I && CuPredMode[ x0 ][ y0 ] != MODE_INTRA ) ) &&    sps_ibc_enabled_flag )    pred_mode_ibc_flag ae(v)  }  if( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) {   if( sps_pcm_enabled_flag &&    cbWidth >= MinIpcmCbSizeY && cbWidth <= MaxIpcmCbSizeY &&    cbHeight >= MinIpcmCbSizeY && cbHeight <= MaxIpcmCbSizeY )    pcm_flag[ x0 ][ y0 ] ae(v)   if( pcm_flag[ x0 ][ y0 ] ) {    while( !byte_aligned( ) )     pcm_alignment_zero_bit f(1)    pcm_sample( cbWidth, cbHeight, treeType)   } else {    if( treeType = = SINGLE_TREE | | treeType = = DUAL_TREE_LUMA ) {     if( Abs( Log2( cbWidth ) − Log2( cbHeight ) ) <= 2 )      intra_lwip_flag[ x0 ][ y0 ] ae(v)     if( intra_lwip_flag[ x0 ][ y0 ] ) {       intra_lwip_mpm_flag[ x0 ][ y0 ] ae(v)      if( intra_lwip_mpm_flag[ x0 ][ y0 ] )       intra_lwip_mpm_idx[ x0 ][ y0 ] ae(v)      else       intra_lwip_mpm_remainder[ x0 ][ y0 ] ae(v)     } else {      if( ( y0 % CtbSizeY ) > 0 )       intra_luma_ref_idx[ x0 ][ y0 ] ae(v)      if (intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&       ( cbWidth <= MaxTbSizeY | | cbHeight <= MaxTbSizeY ) &&       ( cbWidth * cbHeight > MinTbSizeY * MinTbSizeY ))       intra_subpartitions_mode_flag[ x0 ][ y0 ] ae(v)      if( intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 1 &&       cbWidth <= MaxTbSizeY && cbHeight <= MaxTbSizeY )       intra_subpartitions_split_flag[ x0 ][ y0 ] ae(v)      if( intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&       intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 0 )       intra_luma_mpm_flag[ x0 ][ y0 ] ae(v)      if( intra_luma_mpm_flag[ x0 ][ y0 ] )        intra_luma_mpm_idx[ x0 ][ y0 ] ae(v)      else       intra_luma_mpm_remainder[ x0 ][ y0 ] ae(v)    }   }   if( treeType = = SINGLE_TREE | | treeType = = DUAL_TREE_CHROMA )    intra_chroma_pred_mode[ x0 ][ y0 ] ae(v)   }  } else if( treeType != DUAL_TREE_CHROMA ) { /* MODE_INTER or MODE_IBC */   ...

Semantics

<begin>intra_lwip_flag[x0][y0] equal to 1 specifies that the intra prediction type for luma samples is affine linear weighted intra prediction. intra_lwip_flag[x0][y0] equal to 0 specifies that the intra prediction type for luma samples is not affine linear weighted intra prediction. When intra_lwip_flag[x0][y0] is not present, it is inferred to be equal to 0. The syntax elements intra_lwip_mpm_flag[x0][y0], intra_lwip_mpm_idx[x0][y0] and intra_lwip_mpm_remainder [x0][y0] specify the affine linear weighted intra prediction mode for luma samples. The array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture. When intra_lwip_mpm_flag[x0][y0] is equal to 1, the affine linear weighted intra prediction mode is inferred from a neighboring intra-predicted coding unit according to clause 8.4.X.

When intra_lwip_mpm_flag[x0][y0] is not present, it is inferred to be equal to 1.<end>

intra_subpartitions_split_flag[x0][y0] specifies whether the intra subpartitions split type is horizontal or vertical. When intra_subpartitions_split_flag[x0][y0] is not present, it is inferred as follows:

-   -   If intra_lwip_flag[x0][y0] is equal to 1,         intra_subpartitions_split_flag[x0][y0] is inferred to be equal         to 0.     -   Otherwise, the following applies:         -   If cbHeight is greater than MaxTbSizeY,             intra_subpartitions_split_flag[x0][y0] is inferred to be             equal to 0.         -   Otherwise (cbWidth is greater than MaxTbSizeY),             intra_subpartitions_split_flag[x0][y0] is inferred to be             equal to 1.

Decoding Process 8.4.1 General Decoding Process for Coding Units Coded in Intra Prediction Mode

Inputs to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the         current coding block relative to the top-left luma sample of the         current picture,     -   a variable cbWidth specifying the width of the current coding         block in luma samples,     -   a variable cbHeight specifying the height of the current coding         block in luma samples,     -   a variable treeType specifying whether a single or a dual tree         is used and if a dual tree is used, it specifies whether the         current tree corresponds to the luma or chroma components.         Output of this process is a modified reconstructed picture         before in-loop filtering.         The derivation process for quantization parameters as specified         in clause 8.7.1 is invoked with the luma location (xCb, yCb),         the width of the current coding block in luma samples cbWidth         and the height of the current coding block in luma samples         cbHeight, and the variable treeType as inputs.         When treeType is equal to SINGLE_TREE or treeType is equal to         DUAL_TREE_LUMA, the decoding process for luma samples is         specified as follows:     -   If pcm_flag[xCb][yCb] is equal to 1, the reconstructed picture         is modified as follows:

S _(L)[xCb+i][yCb+j]=pcm_sample_luma[(cbHeight*j)+i]<<(BitDepth_(γ)−PcmBitDepth_(γ)), with i=0 . . . cbWidth−1,j=0 . . . cbHeight−1  (8-6)

-   -   Otherwise, the following applies:     -   1. The luma intra prediction mode is derived as follows:         -   If intra_lwip_flag[xCb][yCb] is equal to 1, the derivation             process for the affine linear weighted intra prediction mode             as specified in clause 8.4.X is invoked with the luma             location (xCb, yCb), the width of the current coding block             in luma samples cbWidth and the height of the current coding             block in luma samples cbHeight as input.         -   Otherwise, the derivation process for the luma intra             prediction mode as specified in clause 8.4.2 is invoked with             the luma location (xCb, yCb), the width of the current             coding block in luma samples cbWidth and the height of the             current coding block in luma samples cbHeight as input.     -   2. The general decoding process for intra blocks as specified in         clause 8.4.4.1 is invoked with the luma location (xCb, yCb), the         tree type treeType, the variable nTbW set equal to cbWidth, the         variable nTbH set equal to cbHeight, the variable predModeIntra         set equal to IntraPredModeY[xCb][yCb], and the variable cldx set         equal to 0 as inputs, and the output is a modified reconstructed         picture before in-loop filtering.         <begin>

8.4.X Derivation Process for Affine Linear Weighted Intra Prediction Mode

Input to this Process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the         current luma coding block relative to the top-left luma sample         of the current picture,     -   a variable cbWidth specifying the width of the current coding         block in luma samples,     -   a variable cbHeight specifying the height of the current coding         block in luma samples.         In this process, the affine linear weighted intra prediction         mode IntraPredModeY[xCb][yCb] is derived.         IntraPredModeY[xCb][yCb] is derived by the following ordered         steps:     -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are         set equal to (xCb−1, yCb) and (xCb, yCb−1), respectively.     -   2. For X being replaced by either A or B, the variables         candLwipModeX are derived as follows:         -   The availability derivation process for a block as specified             in clause 6.4.X [Ed. (BB): Neighboring blocks availability             checking process tbd] is invoked with the location (xCurr,             yCurr) set equal to (xCb, yCb) and the neighboring location             (xNbY, yNbY) set equal to (xNbX, yNbX) as inputs, and the             output is assigned to availableX.         -   The candidate affine linear weighted intra prediction mode             candLwipModeX is derived as follows:             -   If one or more of the following conditions are true,                 candLwipModeX is set equal to −1.                 -   The variable availableX is equal to FALSE.                 -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                     and mh_intra_flag[xNbX][yNbX] is not equal to 1.                 -   pcm_flag[xNbX][yNbX] is equal to 1.                 -   X is equal to B and yCb−1 is less than                     ((yCb>>CtbLog2SizeY)<<CtbLog2SizeY).             -   Otherwise, the following applies:                 -   The size type derivation process for a block as                     specified in clause 8.4.X.1 is invoked with the                     width of the current coding block in luma samples                     cbWidth and the height of the current coding block                     in luma samples cbHeight as input, and the output is                     assigned to variable sizeId.                 -   If intra_lwip_flag[xNbX][yNbX] is equal to 1, the                     size type derivation process for a block as                     specified in clause 8.4.X.1 is invoked with the                     width of the neighboring coding block in luma                     samples nbWidthX and the height of the neighboring                     coding block in luma samples nbHeightX as input, and                     the output is assigned to variable sizeIdX.                 -    If sizeId is equal to sizeIdX, candLwipModeX is set                     equal to IntraPredModeY[xNbX][yNbX].                 -    Otherwise, candLwipModeX is set equal to −1.                 -   Otherwise, candLwipModeX is derived using                     IntraPredModeY[xNbX][yNbX] and sizeId as specified                     in Table 8-X1.     -   3. The candLwipModeList[x] with x=0 . . . 2 is derived as         follows, using lwipMpmCand[sizeId] as specified in Table 8-X2:         -   If candLwipModeA and candLwipModeB are both equal to −1, the             following applies:

candLwipModeList[0]=lwipMpmCand[sizeId][0]  (8-X1)

candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X2)

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X3)

-   -   -   Otherwise, the following applies:             -   If candLwipModeA is equal to candLwipModeB or if either                 candLwipModeA or candLwipModeB is equal to −1, the                 following applies:

candLwipModeList[0]=(candLwipModeA!=−1)?candLwipModeA:candLwipModeB   (8-X4)

-   -   -   -   -   If candLwipModeList[0] is equal to                     lwipMpmCand[sizeId][0], the following applies:

candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X5)

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X6)

-   -   -   -   -   Otherwise, the following applies:

candLwipModeList[1]=lwipMpmCand[sizeId][0]  (8-X7)

candLwipModeList[2]=(candLwipModeList[0]!=lwipMpmCand[sizeId][1])?lwipMpmCand[sizeId][1]:lwipMpmCand[sizeId][2]  (8-X8)

-   -   -   Otherwise, the following applies:

candLwipModeList[0]=candLwipModeA  (8-X9)

candLwipModeList[1]=candLwipModeB  (8-X10)

-   -   -   -   If candLwipModeA and candLwipModeB are both not equal to                 lwipMpmCand[sizeId][0], the following applies:

candLwipModeList[2]=lwipMpmCand[sizeId][0]  (8-X11)

-   -   -   -   Otherwise, the following applies:                 -   -If-candLwipModeA and candLwipModeB are both not                     equal to lwipMpmCand[sizeId ][1], the following                     applies:

candLwipModeList[2]=lwipMpmCand[sizeId][1]  (8-X12)

-   -   -   -   -   Otherwise, the following applies:

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X13)

-   -   4. IntraPredModeY[xCb][yCb] is derived by applying the following         procedure:         -   If intra_lwip_mpm_flag[xCb][yCb] is equal to 1, the             IntraPredModeY[xCb][yCb] is set equal to             candLwipModeList[intra_lwip_mpm_idx[xCb][yCb]].         -   Otherwise, IntraPredModeY[xCb][yCb] is derived by applying             the following ordered steps:             -   1. When candLwipModeList[i] is greater than                 candLwipModeList[j] for i=0..1 and for each i,                 j=(i+1)..2, both values are swapped as follows:

(candLwipModeList[i ], candLwipModeList[j])=Swap(candLwipModeList[i ], candLwipModeList[j])  (8-X14)

-   -   -   -   2. IntraPredModeY[xCb][yCb] is derived by the following                 ordered steps:                 -   i. IntraPredModeY[xCb][yCb] is set equal to                     intra_lwip_mpm_remainder[xCb][yCb].                 -   ii. For i equal to 0 to 2, inclusive, when                     IntraPredModeY[xCb][yCb] is greater than or equal to                     candLwipModeList[i], the value of IntraPredMode                     Y[xCb][yCb] is incremented by one.                     The variable IntraPredModeY[x][y] with                     x=xCb..xCbcbWidth−1 and y=yCb..yCb+cbHeight−1 is set                     to be equal to IntraPredModeY[xCb][yCb].                     8.4.X.1 Derivation process for prediction block size                     type                     Input to this process are:

    -   a variable cbWidth specifying the width of the current coding         block in luma samples,

    -   a variable cbHeight specifying the height of the current coding         block in luma samples.         Output of this process is a variable sizeId.         The variable sizeId is derived as follows:

    -   If both cbWidth and cbHeight are equal to 4, sizeId is set equal         to 0.

    -   Otherwise, if both cbWidth and cbHeight are less than or equal         to 8, sizeId is set equal to 1.

    -   Otherwise, sizeId is set equal to 2.

TABLE 8-X1 Specification of mapping between intra prediction and affine linear weighted intra prediction modes block size type sizeId IntraPredModeY[ xNbX ][ yNbX ] 0 1 2 0  17 0 5 1  17 0 1 2, 3 17 10 3 4, 5 9 10 3 6, 7 9 10 3 8, 9 9 10 3 10, 11 9 10 0 12, 13 17 4 0 14, 15 17 6 0 16, 17 17 7 4 18, 19 17 7 4 20, 21 17 7 4 22, 23 17 5 5 24, 25 17 5 1 26, 27 5 0 1 28, 29 5 0 1 30, 31 5 3 1 32, 33 5 3 1 34, 35 34 12 6 36, 37 22 12 6 38, 39 22 12 6 40, 41 22 12 6 42, 43 22 14 6 44, 45 34 14 10 46, 47 34 14 10 48, 49 34 16 9 50, 51 34 16 9 52, 53 34 16 9 54, 55 34 15 9 56, 57 34 13 9 58, 59 26 1 8 60, 61 26 1 8 62, 63 26 1 8 64, 65 26 1 8 66    26 1 8

TABLE 8-X2 Specification of affine linear weighted intra prediction candidate modes candidate mode 0 1 2 lwipMpmCand[ 0 ] 17 34 5 lwipMpmCand[ 1 ] 0 7 16 lwipMpmCand[ 2 ] 1 4 6 <end>

8.4.2. Derivation Process for Luma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the         current luma coding block relative to the top-left luma sample         of the current picture,     -   a variable cbWidth specifying the width of the current coding         block in luma samples,     -   a variable cbHeight specifying the height of the current coding         block in luma samples.

In this process, the luma intra prediction mode IntraPredModeY[xCb][yCb] is derived.

-   Table 8-1 specifies the value for the intra prediction mode     IntraPredModeY[xCb][yCb] and the associated names.

TABLE 8-1 Specification of intra prediction mode and associated names Intra prediction mode Associated name 0   INTRA_PLANAR 1   INTRA_DC 2..66 INTRA_ANGULAR2..INTRA_ANGULAR66 81..83 INTRA_LT_CCLM, INTRA_L_CCLM, INTRA_T_CCLM

-   -   NOTE—: The intra prediction modes INTRA_LT_CCLM, INTRA__L_CCLM         and INTRA__T_CCLM are only applicable to chroma components.

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

-   -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are         set equal to (xCb−1, yCb+cbHeight−1) and (xCb+cbWidth−1, yCb−1),         respectively.     -   2. For X being replaced by either A or B, the variables         candIntraPredModeX are derived as follows:         -   The availability derivation process for a block as specified             in clause <begin>6.4.X [Ed. (BB): Neighboring blocks             availability checking process tbd]<end> is invoked with the             location (xCurr, yCurr) set equal to (xCb, yCb) and the             neighboring location (xNbY, yNbY) set equal to (xNbX, yNbX)             as inputs, and the output is assigned to availableX.         -   The candidate intra prediction mode candIntraPredModeX is             derived as follows:             -   If one or more of the following conditions are true,                 candIntraPredModeX is set equal to INTRA_PLANAR.                 -   The variable availableX is equal to FALSE.                 -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                     and ciip_flag[xNbX][yNbX] is not equal to 1.                 -   pcm_flag[xNbX][yNbX] is equal to 1.                 -   X is equal to B and yCb−1 is less than                     ((yCb>>CtbLog2SizeY)<<CtbLog2SizeY).             -   Otherwise, candIntraPredModeX is derived as follows:                 -   If intra_lwip_flag[xCb][yCb] is equal to 1,                     candIntraPredModeX is derived by the following                     ordered steps:                 -    i. The size type derivation process for a block as                     specified in clause 8.4.X.1 is invoked with the                     width of the current coding block in luma samples                     cbWidth and the height of the current coding block                     in luma samples cbHeight as input, and the output is                     assigned to variable sizeId.                 -    ii. candIntraPredModeX is derived using                     IntraPredModeY[xNbX][yNbX] and sizeId as specified                     in Table 8-X3.             -   Otherwise, candIntraPredModeX is set equal to                 IntraPredModeY[xNbX][yNbX].     -   3. The variables ispDefaultMode1 and ispDefaultMode2 are defined         as follows:         -   If IntraSubPartitionsSplitType is equal to ISP_HOR_SPLIT,             ispDefaultMode1 is set equal to INTRA_ANGULAR18 and             ispDefaultMode2 is set equal to INTRA_ANGULAR5.         -   Otherwise, ispDefaultMode1 is set equal to INTRA_ANGULAR50             and ispDefaultMode2 is set equal to INTRA_ANGULAR63.

TABLE 8-X3 Specification of mapping between affine linear weighted intra prediction and intra prediction modes block size type sizeId IntraPredModeY[ xNbX ][ yNbX ] 0 1 2 0 0 0 1 1 18 1 1 2 18 0 1 3 0 1 1 4 18 0 18 5 0 22 0 6 12 18 1 7 0 18 0 8 18 1 1 9 2 0 50 10 18 1 0 11 12 0 12 18 1 13 18 0 14 1 44 15 18 0 16 18 50 17 0 1 18 0 0 19 50 20 0 21 50 22 0 23 56 24 0 25 50 26 66 27 50 28 56 29 50 30 50 31 1 32 50 33 50 34 50

8.4.3 Derivation Process for Chroma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the         current chroma coding block relative to the top-left luma sample         of the current picture,     -   a variable cbWidth specifying the width of the current coding         block in luma samples,     -   a variable cbHeight specifying the height of the current coding         block in luma samples.

In this process, the chroma intra prediction mode IntraPredModeC[xCb][yCb] is derived.

The corresponding luma intra prediction mode lumaIntraPredMode is derived as follows:

-   -   If intra_lwip_flag[xCb][yCb] is equal to 1, lumaIntraPredMode is         derived by the following ordered steps:         -   i. The size type derivation process for a block as specified             in clause 8.4.X.1 is invoked with the width of the current             coding block in luma samples cbWidth and the height of the             current coding block in luma samples cbHeight as input, and             the output is assigned to variable sizeId.         -   ii. The luma intra prediction mode is derived using             IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] and sizeId as             specified in Table 8-X3 and assigning the value of             candIntraPredModeX to lumaIntraPredMode.     -   Otherwise, lumaIntraPredMode is set equal to         IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

The chroma intra prediction mode IntraPredModeC[xCb][yCb] is derived using intra_chroma_pred_mode[xCb][yCb] and lumaIntraPredMode as specified in Table 8-2 and Table 8-3.

. . . xxx. Intra Sample Prediction <begin>

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left         sample of the current transform block relative to the top-left         sample of the current picture,     -   a variable predModeIntra specifying the intra prediction mode,     -   a variable nTbW specifying the transform block width,     -   a variable nTbH specifying the transform block height,     -   a variable nCbW specifying the coding block width,     -   a variable nCbH specifying the coding block height,     -   a variable cldx specifying the colour component of the current         block.

Outputs of this process are the predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The predicted samples predSamples[x][y] are derived as follows:

-   -   If intra_lwip_flag[xTbCmp][yTbCmp] is equal to 1 and cldx is         equal to 0, the affine linear weighted intra sample prediction         process as specified in clause 8.4.4.2.X1 is invoked with the         location (xTbCmp, yTbCmp), the intra prediction mode         predModeIntra, the transform block width nTbW and height nTbH as         inputs, and the output is predSamples.     -   Otherwise, the general intra sample prediction process as         specified in clause 8.4.4.2.X1. is invoked with the location         (xTbCmp, yTbCmp), the intra prediction mode predModeIntra, the         transform block width nTbW and height nTbH, the coding block         width nCbW and height nCbH, and the variable cldx as inputs, and         the output is predSamples.

8.4.4.2.X1Affine Linear Weighted Intra Sample Prediction

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left         sample of the current transform block relative to the top-left         sample of the current picture,     -   a variable predModeIntra specifying the intra prediction mode,     -   a variable nTbW specifying the transform block width,     -   a variable nTbH specifying the transform block height.

Outputs of this process are the predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The size type derivation process for a block as specified in clause 8.4.X.1 is invoked with the transform block width nTbW and the transform block height nTbH as input, and the output is assigned to variable sizeId.

Variables numModes, boundarySize, predW, predH and predC are derived using sizeId as specified in Table 8-X4.

TABLE 8-X4 Specification of number of modes, boundary sample size and prediction sizes depending on sizeId sizeId numModes boundarySize predW predH predC 0 35 2 4 4 4 1 19 4 4 4 4 2 11 4 Min( nTbW, 8 ) Min( nTbH, 8 ) 8

The flag isTransposed is derived as follows:

isTransposed=(predModeIntra>(numModes/2))?1:0  (8-X15)

The flags needUpsBdryHor and needUpsBdryVer are derived as follows:

needUpsBdryHor=(nTbW>predW)?TRUE:FALSE  (8-X16)

needUpsBdryVer=(nTbH>predH)?TRUE:FALSE  (8-X17)

The variables upsBdryW and upsBdryH are derived as follows:

upsBdryW=(nTbH>nTbW)?nTbW:predW  (8-X18)

upsBdryH=(nTbH>nTbW)?predH:nTbH  (8-X19)

The variables lwipW and lwipH are derived as follows:

lwipW=(isTransposed==1)?predH:predW  (8-X20)

lwipH=(isTransposed==1)?predW:predH  (8-X21)

For the generation of the reference samples refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1, the reference sample derivation process as specified in clause 8.4.4.2.X2 is invoked with the sample location (xTbCmp, yTbCmp), the transform block width nTbW, the transform block height nTbH as inputs, and top and left reference samples refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1, respectively, as outputs.

For the generation of the boundary samples p[x] with x=0 . . . 2*boundarySize−1, the following applies:

-   -   The boundary reduction process as specified in clause 8.4.4.2.X3         is invoked for the top reference samples with the block size         nTbW, the reference samples refT, the boundary size         boundarySize, the upsampling boundary flag needUpsBdryVer, and         the upsampling boundary size upsBdryW as inputs, and reduced         boundary samples redT[x] with x=0 . . . boundarySize−1 and         upsampling boundary samples upsBdryT[x] with x=0 . . .         upsBdryW−1 as outputs.     -   The boundary reduction process as specified in clause 8.4.4.2.X3         is invoked for the left reference samples with the block size         nTbH, the reference samples refL, the boundary size         boundarySize, the upsampling boundary flag needUpsBdryHor, and         the upsampling boundary size upsBdryH as inputs, and reduced         boundary samples redL[x] with x=0 . . . boundarySize−1 and         upsampling boundary samples upsBdryL[x] with x=0 . . .         upsBdryH−1 as outputs.     -   The reduced top and left boundary samples redT and redL are         assigned to the boundary sample array p as follows:         -   If isTransposed is equal to 1, p[x] is set equal to redL[x]             with x=0 . . . boundarySize−1 and p[x+boundarySize] is set             equal to redT[x] with x=0 . . . boundarySize−1.         -   Otherwise, p[x] is set equal to redT[x] with x=0 . . .             boundarySize−1 and p[x+boundarySize] is set equal to redL[x]             with x=0 . . . boundarySize−1.

For the intra sample prediction process according to predModeIntra, the following ordered steps apply:

-   -   1. The affine linear weighted samples predLwip[x][y], with x=0 .         . . lwipW−1, y=0 . . . lwipH−1 are derived as follows:         -   The variable modeId is derived as follows:

modeId=predModeIntra−(isTransposed==1)?(numModes/2):0  (8-X22)

-   -   -   The weight matrix mWeight[x][y] with x=0 . . .             2*boundarySize−1, y=0 . . . predC*predC−1 is derived using             sizeId and modeId as specified in Table 8-XX [TBD: add             weight matrices].         -   The bias vector vBias[y] with y=0 . . . predC*predC−1 is             derived using sizeId and modeId as specified in Table 8-XX             [TBD: add bias vectors].         -   The variable sW is derived using sizeId and modeId as             specified in Table 8-X5.         -   The affine linear weighted samples predLwip[x][y], with x=0             . . . lwipW−1, y=0 . . . lwipH−1 are derived as follows:

$\begin{matrix} {\mspace{79mu}{{oW} = {1\text{<<}\left( {{sW} - 1} \right)}}} & \left( {8\text{-}{X23}} \right) \\ {\mspace{79mu}{{sB} = {{BitDepth}_{Y} - 1}}} & \left( {8\text{-}{X24}} \right) \\ {\mspace{79mu}{{i{ncW}} = {{\left( {{predC} > {lwipW}} \right)?2}\text{:}1}}} & \left( {8\text{-}{X25}} \right) \\ {\mspace{79mu}{{{i{nc}}\; H} = {{\left( {{predC} > {lwipH}} \right)?2}\text{:}1}}} & \left( {8\text{-}{X26}} \right) \\ {{{{predLwip}\lbrack x\rbrack}\lbrack y\rbrack} = {\left( {\left( {\sum\limits_{i = 0}^{{2*{boundarySize}} - 1}\;{{{{mWeight}\lbrack i\rbrack}\left\lbrack {{y*{incH}*{predC}} + {x*{incW}}} \right\rbrack}*{p\lbrack i\rbrack}}} \right) + \left( {{{vBias}\left\lbrack {{y*{incH}*{predC}} + {x*{incW}}} \right\rbrack}{\operatorname{<<}{sB}}} \right) + {oW}} \right)\text{>>}{sW}}} & \left( {8\text{-}{X27}} \right) \end{matrix}$

-   -   2. The predicted samples predSamples[x][y], with x=0 . . .         nTbW−1, y=0 . . . nTbH−1 are derived as follows:         -   When isTransposed is equal to 1, predLwip[x][y], with x=0 .             . . predW−1, y=0 . . . predH−1 is set equal to             predLwip[y][x].         -   If needUpsBdryVer is equal to TRUE or needUpsBdryHor is             equal to TRUE, the prediction upsampling process as             specified in clause 8.4.4.2.X4 is invoked with the input             block width predW, the input block height predH, affine             linear weighted samples predLwip, the transform block width             nTbW, the transform block height nTbH, the upsampling             boundary width upsBdryW, the upsampling boundary height             upsBdryH, the top upsampling boundary samples upsBdryT, and             the left upsampling boundary samples upsBdryL as inputs, and             the output is the predicted sample array predSamples.         -   Otherwise, predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .             . nTbH−1 is set equal to predLwip[x][y].

TABLE 8-X5 Specification of weight shifts sW depending on sizeId and modeId modeId sizeId 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 0 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 1 8 8 8 9 8 8 8 8 9 8 2 8 8 8 8 8 8

8.4.4.2.X2Reference Sample Derivation Process

Inputs to this process are:

-   -   a sample location (xTbY, yTbY) specifying the top-left luma         sample of the current transform block relative to the top-left         luma sample of the current picture,     -   a variable nTbW specifying the transform block width,     -   a variable nTbH specifying the transform block height.

Outputs of this process are the top and left reference samples refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1, respectively.

The neighboring samples refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1 are constructed samples prior to the in-loop filter process and derived as follows:

-   -   The top and left neighboring luma locations (xNbT, yNbT) and         (xNbL, yNbL) are specified by:

(xNbT,yNbT)=(xTbY+x,yTbY−1)  (8-X28)

(xNbL,yNbL)=(xTbY−1,yTbY+y)  (8-X28)

-   -   The availability derivation process for a block as specified in         clause 6.4.X [Ed. (BB): Neighboring blocks availability checking         process tbd] is invoked with the current luma location (xCurr,         yCurr) set equal to (xTbY, yTbY) and the top neighboring luma         location (xNbT, yNbT) as inputs, and the output is assigned to         availTop[x] with x=0 . . . nTbW−1.     -   The availability derivation process for a block as specified in         clause 6.4.X [Ed. (BB): Neighboring blocks availability checking         process tbd] is invoked with the current luma location (xCurr,         yCurr) set equal to (xTbY, yTbY) and the left neighboring luma         location (xNbL, yNbL) as inputs, and the output is assigned to         availLeft[y] with y=0 . . . nTbH−1.     -   The top reference samples refT[x] with x=0 . . . nTbW−1 are         derived as follows:         -   If all availTop[x] with x=0 . . . nTbW−1 are equal to TRUE,             the sample at the location (xNbT, yNbT) is assigned to             refT[x] with x=0 . . . nTbW−1.         -   Otherwise, if availTop[0] is equal to FALSE, all refT[x]             with x=0 . . . nTbW−1 are set equal to I<<(BitDepthγ−1).         -   Otherwise, reference samples refT[x] with x=0 . . . nTbW−1             are derived by the following ordered steps:             -   1. The variable lastT is set equal to the position x of                 the first element in the sequence availTop[x] with x=1.                 . . nTbW−1 that is equal to FALSE.             -   2. For every x=0 . . . lastT−1, the sample at the                 location (xNbT, yNbT) is assigned to refT[x].             -   3. For every x=lastT. . . nTbW−1, refT[x] is set equal                 to refT[lastT−1].     -   The left reference samples refL[y] with x=0 . . . nTbH−1 are         derived as follows:         -   If all availLeft[y] with yz=0 . . . nTbH−1 are equal to             TRUE, the sample at the location (xNbL, yNbL ) is assigned             to refL[y] with y=0 . . . nTbH −1.         -   Otherwise, if availLeft[0] is equal to FALSE, all refL[y]             with y=0 . . . nTbH−1 are set equal to 1<<(BitDepth_(Y)−1).         -   Otherwise, reference samples refL[y] with y=0 . . . nTbH−1             are derived by the following ordered steps:             -   1. The variable lastL is set equal to the position y of                 the first element in the sequence availLeft[y] with y=1                 . . . nTbH−1 that is equal to FALSE.             -   2. For every y=0 . . . lastL−1, the sample at the                 location (xNbL, yNbL) is assigned to refL[y].             -   3.For every y=lastL . . . nTbH−1, refL[y] is set equal                 to refL[lastL−1].                 Specification of the boundary reduction process

Inputs to this process are:

-   -   a variable nTbX specifying the transform block size,     -   reference samples refX[x] with x=0 . . . nTbX−1,     -   a variable boundarySize specifying the downsampled boundary         size,     -   a flag needUpsBdryX specifying whether intermediate boundary         samples are required for upsampling,     -   a variable upsBdrySize specifying the boundary size for         upsampling.

Outputs of this process are the reduced boundary samples redX[x] with x=0 . . . boundarySize−1 and upsampling boundary samples upsBdryX[x] with x=0 . . . upsBdrySize−1.

The upsampling boundary samples upsBdryX[x] with x=0 . . . upsBdrySize−1 are derived as follows:

-   -   If needUpsBdryX is equal to TRUE and upsBdrySize is less than         nTbX, the following applies:

uDwn=nTbX/upsBdrySize  (8-X30)

upsBdryX[x]=(Σ_(i=0) ^(uDwn-1)refX[x*uDwn+i]+(1<<(Log2(uDwn)−1)))>>Log2(uDwn)   (8-X31)

-   -   Otherwise (upsBdrySize is equal to nTbX), upsBdryX[x] is set         equal to refX[x].

The reduced boundary samples redX[x] with x=0 . . . boundarySize−1 are derived as follows:

-   -   If boundarySize is less than upsBdrySize, the following applies:

bDwn=upsBdrySize/boundarySize  (8-X32)

redX[x]=(Σ_(i=0) ^(bDwn-1)upsBdryX[x*bDwn+i]+(1<<(Log2(bDwn)−1)))>>Log2(bDwn)   (8-X33)

-   -   Otherwise (boundarySize is equal to upsBdrySize), redX[x] is set         equal to upsBdryX[x].

8.4.4.2.X4Specification of the Prediction Upsampling Process

Inputs to this process are:

-   -   a variable predW specifying the input block width,     -   a variable predH specifying the input block height,     -   affine linear weighted samples predLwip[x][y], with x=0 . . .         predW−1, y=0 . . . predH−1,     -   a variable nTbW specifying the transform block width,     -   a variable nTbH specifying the transform block height,     -   a variable upsBdryW specifying the upsampling boundary width,     -   a variable upsBdryH specifying the upsampling boundary height,     -   top upsampling boundary samples upsBdryT[x] with x=0 . . .         upsBdryW−1,     -   left upsampling boundary samples upsBdryL[x] with x=0 . . .         upsBdryH−1.

Outputs of this process are the predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The sparse predicted samples predSamples[m][n] are derived from predLwip[x][y], with x=0 . . . predW−1, y=0 . . . predH−1 as follows:

upHor=nTbW/predW  (8-X34)

upVer=nTbH/predH  (8-X35)

predSamples[(x+1)*upHor−1][(y+1)*upVer−1]=predLwip[x][y]  (8-X36)

The top boundary samples upsBdryT[x] with x=0 . . . upsBdryW−1 are assigned to predSamples[m][−1] as follows:

predSamples[(x−1)*(nTbW/upsBdryW)−1][−1]=upsBdryL[y]  (8-X37)

The left boundary samples upsBdryL[y] with y=0 . . . upsBdryH−1 are assigned to predSamples[−1][n] as follows:

predSamples[−1][(y+1)*(nTbH/upsBdryH)−1]=upsBdryL[y]  (8-X38)

The predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:

-   -   If nTbH is greater than nTbW, the following ordered steps apply:     -   1. When upHor is greater than 1, horizontal upsampling for all         sparse positions (xHor, yHor)=(m*upHor−1, n*upVer−1) with m=0 .         . . predW−1, n=1 . . . predH is applied with dX=1 . . . upHor−1         as follows:

predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor])/upHor  (8-X39)

-   -   2. Vertical upsampling for all sparse positions (xVer, yVer)=(m,         n*upVer−1) with m=0 . . . nTbW−1, n=0 . . . predH−1 is applied         with dY=1 . . . upVer−1 as follows:

predSamples[xVer][yVer+dY]=(( upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer])/upVer  (8-X40)

-   -   Otherwise, the following ordered steps apply:     -   1. When upVer is greater than 1, vertical upsampling for all         sparse positions (xVer, yVer)=(m*upHor−1, n*upVer−1) with m=1 .         . . predW, n=0 . . . predH−1 is applied with dY=1 . . . upVer−1         as specified in (8-X40).     -   2. Horizontal upsampling for all sparse positions (xHor,         yHor)=(m*upHor−1, n) with m=0 . . . predW−1, n=0 . . . nTbH−1 is         applied with dX=1 . . . upHor−1 as specified in (8-X39).         <end>

TABLE 9-9 Syntax elements and associated binarizations Binarization Syntax structure Syntax element Process Input parameters coding_unit( ) cu_skip_flag[ ][ ] FL cMax = 1 pred_mode_ibc_flag FL cMax = 1 pred_mode_flag FL cMax = 1 <begin>intra_lwip_flag[ ][ ] FL cMax = 1 intra_lwip_mpm_flag[ ][ ] FL cMax = 1 intra_lwip_mpm_idx[ ][ ] TR cMax = 2, cRiceParam = 0 intra_lwip_mpm_remainder[ ][ ] FL cMax = (cbWidth = = 4 && cbHeight = = 4) ? 31 : ( (cbWidth <= 8 && cbHeight <= 8) ? 15 : 7) ...

TABLE 9-15 Assignment of ctxInc to syntax elements with context coded bins binldx Syntax element 0 1 2 3 4 >= 5 ... terminate na na na na na intra_lwip_flag[ ][ ] (Abs ( Log2 (cbWidth) - na na na na na Log2 (cbHeight) ) > 1) ? 3 : ( 0, 1, 2 (clause 9.5.4.2.2) ) intra_lwip_mpm_flag[ ][ ] 0 na na na na na intra_lwip_mpm_idx[ ][ ] bypass bypass na na na na intra_lwip_mpm_remainder[ ][ ] bypass bypass bypass bypass bypass na

TABLE 9-16 Specification of ctxInc using left and above syntax elements Syntax element condL condA ctxSetIdx ... intra_lwip_flag[ x0 ][ y0 ] intra_lwip_flag[ xNbL ][ yNbL ] intra_lwip_flag[ xNbA ][ yNbA ] 0 ... <end>

Summary of ALWIP

For predicting the samples of a rectangular block of width W and height H, affine linear weighted intra prediction (ALWIP) takes one line of H reconstructed neighboring boundary samples left of the block and one line of W reconstructed neighboring boundary samples above the block as input. If the reconstructed samples are unavailable, they are generated as it is done in the conventional intra prediction. ALWIP is only applied to luma intra block. For chroma intra block, the conventional intra coding modes are applied.

The generation of the prediction signal is based on the following three steps:

-   -   1. Out of the boundary samples, four samples in the case of         W=H=4 and eight samples in all other cases are extracted by         averaging.     -   2. A matrix vector multiplication, followed by addition of an         offset, is carried out with the averaged samples as an input.         The result is a reduced prediction signal on a subsampled set of         samples in the original block.     -   3. The prediction signal at the remaining positions is generated         from the prediction signal on the subsampled set by linear         interpolation which is a single step linear interpolation in         each direction.

If an ALWIP mode is to be applied, the index predmode of the ALWIP mode is signaled using a MPM-list with 3 MPMS. Here, the derivation of the MPMs is performed using the intra-modes of the above and the left PU as follows. There are three fixed tables map_angular_to_alwip_(idx), idx ∈ {0,1,2} that assign to each conventional intra prediction mode predmode_(Angular) an ALWIP mode

predmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an index

idx(PU)=idx(W,H)∈{0,1,2}

that indicates from which of the three sets the ALWIP-parameters are to be taken.

If the above Prediction Unit PU_(above) is available, belongs to the same CTU as the current PU and is in intra mode, if idx(PU)=idx(PU above) above) and if ALWIP is applied on PU_(above) with ALWIP-mode predmode_(ALWIP) ^(above), one puts

mode_(ALWIP)^(above) = predmode_(ALWIP)^(above).

If the above PU is available, belongs to the same CTU as the current PU and is in intra mode and if a conventional intra prediction mode predmode_(Angular) ^(above) is applied on the above PU, one puts

mode_(ALWIP) ^(above)=map_angular_to_alwip_(idx(PU) _(above) )[predmode_(Angular) ^(above)].

In all other cases, one puts

mode_(ALWIP) ^(above)=−1

which means that this mode is unavailable. In the same way but without the restriction that the left PU needs to belong to the same CTU as the current PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx ∈{0,1,2} are provided, each of which contains three distinct ALWIP modes. Out of the default list list_(idx(pu)) and the modes mode_(ALWIP) ^(above) and mode_(ALWIP) ^(left), one constructs three distinct MPMs by substituting −1 by default values as well as eliminating repetitions.

For the luma MPM-list derivation, whenever a neighboring luma block is encountered which uses an ALWIP-mode predmode_(ALWIP), this block is treated as if it was using the conventional intra-prediction mode predmode_(Angular).

predmode_(Angular)=map_alwip_to_angular_(idx(pu))[predmode_(ALWIP)]

3 Transform in VVC 3.1 Multiple Transform Selection (MTS)

In addition to DCT-II which has been employed in HEVC, a Multiple Transform Selection (MTS) scheme is used for residual coding both inter and intra coded blocks. It uses multiple selected transforms from the DCT8/DST7. The newly introduced transform matrices are DST-VII and DCT-VIII.

3.2 Reduced Secondary Transform (RST) Proposed in JVET-N0193

Reduced secondary transform (RST) applies 16×16 and 16×64 non-separable transform for 4×4 and 8×8 blocks, respectively. Primary forward and inverse transforms are still performed the same way as two 1-D horizontal/vertical transform passes. Secondary forward and inverse transforms are a separate process step from that of primary transforms. For encoder, primary forward transform is performed first, then followed by secondary forward transform and quantization, and CABAC bit encoding. For decoder, CABAC bit decoding and inverse quantization, then Secondary inverse transform is performed first, then followed by primary inverse transform. RST applies only to intra coded TUs in both intra slice and inter slices.

3.3 A Unified MPM List for Intra Mode Coding in JVET-N0185

A unified 6-MPM list is proposed for intra blocks irrespective of whether Multiple Reference Line (MRL) and Intra sub-partition (ISP) coding tools are applied or not. The MPM list is constructed based on intra modes of the left and above neighboring block as in VTM4.0. Suppose the mode of the left is denoted as Left and the mode of the above block is denoted as Above, the unified MPM list is constructed as follows:

-   -   When a neighboring block is not available, its intra mode is set         to Planar by default.     -   If both modes Left and Above are non-angular modes:     -   a. MPM list→{Planar, DC, V, H, V−4, V+4}     -   If one of modes Left and Above is angular mode, and the other is         non-angular:     -   a. Set a mode Max as the larger mode in Left and Above     -   b. MPM list→{Planar, Max, DC, Max−1, Max+1, Max−2}     -   If Left and Above are both angular and they are different:     -   a. Set a mode Max as the larger mode in Left and Above     -   b. if the difference of mode Left and Above is in the range of 2         to 62, inclusive         -   i. MPM list→{Planar, Left, Above, DC, Max−1, Max+1}     -   c. Otherwise         -   i. MPM list→{Planar, Left, Above, DC, Max−2, Max+2}     -   If Left and Above are both angular and they are the same:     -   a. MPM list→{Planar, Left, Left−1, Left+1, DC, Left−2}

Besides, the first bin of the MPM index codeword is CABAC context coded. In total three contexts are used, corresponding to whether the current intra block is MRL enabled, ISP enabled, or a normal intra block.

The left neighboring block and above neighboring block used in the unified MPM list construction is A2 and B2 as shown in FIG. 10.

One MPM flag is firstly coded. If the block is coded with one of mode in the MPM list, an MPM index is further coded. Otherwise, an index to the remaining modes (excluding MPMs) is coded.

4 Examples of Drawbacks in Existing Implementations

The design of ALWIP in JVET-N0217 has the following problems:

-   -   1) At the March 2019 JVET meeting, a unified 6-MPM list         generation was adopted for MRL mode, ISP mode, and normal intra         mode. But the affine linear weighted prediction mode uses a         different 3-MPM list construction which makes the MPM list         construction complicated. A complex MPM list construction might         compromise the throughput of the decoder, in particular for         small blocks such as 4×4 samples.     -   2) ALWIP is only applied to luma component of the block. For the         chroma component of an ALWP coded block, a chroma mode index is         coded and sent to decoder, which could result in unnecessary         signaling.     -   3) The interactions of ALWIP with other coding tools should be         considered.     -   4) When calculating upsBdryX in upsBdryX[x]=(Σ_(i=0) ^(uDwn-1)         RefX[x*uDwn+i]+(1<<(Log2(uDwn)−1)))>>Log2(uDwn) (8-X31), it is         possible that Log2(uDwn)−1 is equal to −1, while left shifted         with −1 is undefined.     -   5) When upsampling the prediction samples, no rounding is         applied.     -   6) In the deblocking process, ALWIP coded blocks are treated as         normal intra-blocks.

5 Exemplary Methods for Matrix-Based Intra Coding

Embodiments of the presently disclosed technology overcome drawbacks of existing implementations, thereby providing video coding with higher coding efficiencies but lower computational complexity. Matrix-based intra prediction methods for video coding, and as described in the present document, may enhance both existing and future video coding standards, is elucidated in the following examples described for various implementations. The examples of the disclosed technology provided below explain general concepts and are not meant to be interpreted as limiting. In an example, unless explicitly indicated to the contrary, the various features described in these examples may be combined.

In the following discussion, an intra-prediction mode refers to an angular intra prediction mode (including DC, planar, CCLM and other possible intra prediction modes); while an intra mode refers to normal intra mode, or MRL, or ISP or ALWIP.

In the following discussion, “Other intra modes” may refer to one or multiple intra modes except ALWIP, such as normal intra mode, or MRL, or ISP.

In the following discussion, SatShift(x, n) is defined as

${{SatShift}\left( {x,n} \right)} = \left\{ \begin{matrix} {{\left( {x + {{offsset}\; 0}} \right)\operatorname{>>}n}\mspace{14mu}} & {{{if}\mspace{14mu} x} \geq 0} \\ {{- \left( {\left( {{- x} + {{offset}\; 1}} \right)\operatorname{>>}n} \right)}\mspace{14mu}} & {{{if}\mspace{14mu} x} < 0} \end{matrix} \right.$

Shift(x, n) is defined as Shift(x, n)=(x+offset0)>>n.

In one example, offset0 and/or offset1 are set to (1<<n)>>1 or (1<<(n−1)). In another example, offset0 and/or offset1 are set to 0.

In another example, offset0=offset1=((1<<n)>>1)−1 or ((1<<(n−1)))−1.

Clip3(min, max, x) is defined as

${{Clip}\; 3\left( {{Min},{Max},x} \right)} = \left\{ \begin{matrix} {{Min}\mspace{20mu}} & {{{if}\ x} < {Min}} \\ {{Max}\mspace{20mu}} & {{{if}\ x} > {Max}} \\ {x\ } & {Otherwise} \end{matrix} \right.$

MPM List Construction for ALWIP

-   -   1. It is proposed that the whole or partial of the MPM list for         ALWIP may be constructed according to the whole or partial         procedure to construct the MPM list for non-ALWIP intra mode         (such as normal intra mode, MRL, or ISP).         -   a. In one example, the size of the MPM list for ALWIP may be             the same as that of the MPM list for non-ALWIP intra mode.             -   i. For example, the size of MPM list is 6 for both ALWIP                 and non-ALWIP intra modes.         -   b. In one example, the MPM list for ALWIP may be derived             from the MPM list for non-ALWIP intra mode.             -   i. In one example, the MPM list for non-ALWIP intra mode                 may be firstly constructed. Afterwards, partial or all                 of them may be converted to the MPMs which may be                 further added to the MPM list for ALWIP coded blocks.                 -   1) Alternatively, furthermore, when adding a                     converted MPM to the MPM list for ALWIP coded                     blocks, pruning may be applied.                 -   2) Default modes may be added to the MPM list for                     ALWIP coded blocks.                 -    a. In one example, default modes may be added                     before those converted from the MPM list of                     non-ALWIP intra mode.                 -    b. Alternatively, default modes may be added after                     those converted from the MPM list of non-ALWIP intra                     mode.                 -    c. Alternatively, default modes may be added in an                     interleaved way with those converted from the MPM                     list of non-ALWIP intra mode.                 -    d. In one example, the default modes may be fixed                     to be the same for all kinds of blocks.                 -    e. Alternatively, the default modes may be                     determined according to coded information, such as                     availability of neighboring blocks, mode information                     of neighboring blocks, block dimension.             -   ii. In one example, one intra-prediction mode in the MPM                 list for non-ALWIP intra mode may be converted to its                 corresponding ALWIP intra-prediction mode, when it is                 put into the MPM list for ALWIP.                 -   1) Alternatively, all the intra-prediction modes in                     the MPM list for non-ALWIP intra modes may be                     converted to corresponding ALWIP intra-prediction                     modes before being used to construct the MPM list                     for ALWIP.                 -   2) Alternatively, all the candidate intra-prediction                     modes (may include the intra-prediction modes from                     neighboring blocks and default intra-prediction                     modes such as Planar and DC) may be converted to                     corresponding ALWIP intra-prediction modes before                     being used to construct the MPM list for non-ALWIP                     intra modes, if the MPM list for non-ALWIP intra                     modes may be further used to derive the MPM list for                     ALWIP.                 -   3) In one example, two converted ALWIP                     intra-prediction modes may be compared.                 -    a. In one example, if they are the same, only one                     of them may be put into the MPM list for ALWIP.                 -    b. In one example, if they are the same, only one                     of them may be put into the MPM list for non-ALWIP                     intra modes.             -   iii. In one example, K out of S intra-prediction modes                 in the MPM list for non-ALWIP intra modes may be picked                 as the MPM list for ALWIP mode. E.g., K is equal to 3                 and S is equal to 6.                 -   1) In one example, the first K intra-prediction                     modes in the MPM list for non-ALWIP intra modes may                     be picked as the MPM list for ALWIP mode.     -   2. It is proposed that the one or multiple neighboring blocks         used to derive the MPM list for ALWIP may also be used to used         derive the MPM list for non-ALWIP intra modes (such as normal         intra mode, MRL, or ISP).         -   a. In one example, the neighboring block left to the current             block used to derive the MPM list for ALWIP should be the             same as that used to derive the MPM list for non-ALWIP intra             modes.             -   i. Suppose the top-left corner of the current block is                 (xCb, yCb), the width and height of the current block                 are W and H, then in one example, the left neighboring                 block used to derive the MPM list for both ALWIP and                 non-ALWIP intra modes may cover the position (xCb−1,                 yCb). In an alternative example, the left neighboring                 block used to derive the MPM list for both ALWIP and                 non-ALWIP intra modes may cover the position (xCb−1,                 yCb+H−1).             -   ii. For example, the left neighboring block and above                 neighboring block used in the unified MPM list                 construction is A2 and B2 as shown in FIG. 10.         -   b. In one example, the neighboring block above to the             current block used to derive the MPM list for ALWIP should             be the same as that used to derive the MPM list for             non-ALWIP intra modes.             -   i. Suppose the top-left corner of the current block is                 (xCb, yCb), the width and height of the current block                 are W and H, then in one example, the above neighboring                 block used to derive the MPM list for both ALWIP and                 non-ALWIP intra modes may cover the position (xCb,                 yCb−1). In an alternative example, the above neighboring                 block used to derive the MPM list for both ALWIP and                 non-ALWIP intra modes may cover the position (xCb+W−1,                 yCb−1).             -   ii. For example, the left neighboring block and above                 neighboring block used in the unified MPM list                 construction is A1 and B1 as shown in FIG. 10.     -   3. It is proposed that the MPM list for ALWIP may be constructed         in different ways according to the width and/or height of the         current block.         -   a. In one example, different neighboring blocks may be             accessed for different block dimensions.     -   4. It is proposed that the MPM list for ALWIP and the MPM list         for non-ALWIP intra modes may be constructed with the same         procedure but with different parameters.         -   a. In one example, K out of S intra-prediction modes in the             MPM list construction procedure of non-ALWIP intra modes may             be derived for the MPM list used in ALWIP mode. E.g., K is             equal to 3 and S is equal to 6.             -   i. In one example, the first K intra-prediction modes in                 the MPM list construction procedure may be derived for                 the MPM list used in ALWIP mode.         -   b. In one example, the first mode in the MPM list may be             different.             -   i. For example, the first mode in the MPM list for                 non-ALWIP intra modes may be Planar, but it may be a                 Mode X0 in the MPM list for ALWIP.                 -   1) In one example, X0 may be the ALWIP                     intra-prediction mode converted from Planar.         -   c. In one example, stuffing modes in the MPM list may be             different.             -   i. For example, the first three stuffing modes in the                 MPM list for non-ALWIP intra modes may be DC, Vertical                 and Horizontal, but they may be Mode X1, X2, X3 in the                 MPM list for ALWIP.                 -   1) In one example, X1, X2, X3 may be different for                     different sizeId.             -   ii. In one example, the number of stuffing mode may be                 different.         -   d. In one example, neighboring modes in the MPM list may be             different.             -   i. For example, the normal intra-prediction modes of                 neighboring blocks are used to construct the MPM list                 for non-ALWIP intra modes. And they are converted to                 ALWIP intra-prediction modes to construct the MPM list                 for ALWIP mode.         -   e. In one example, the shifted modes in the MPM list may be             different.             -   i. For example, X+K0 where X is a normal                 intra-prediction mode and K0 is an integer may be put                 into the MPM list for non-ALWIP intra modes. And Y+K1                 where Y is an ALWIP intra-prediction mode and K1 is an                 integer may be put into the MPM list for ALWIP, where K0                 may be different from K1.                 -   1) In one example, K1 may depend on the width and                     height.     -   5. It is proposed that a neighboring block is treated as         unavailable if it is coded with ALWIP when constructing the MPM         list for the current block with non-ALWIP intra modes.         -   a. Alternatively, a neighboring block is treated as being             coded with a predefined intra-prediction mode (such as             Planar) if it is coded with ALWIP when constructing the MPM             list for the current block with non-ALWIP intra modes.     -   6. It is proposed that a neighboring block is treated as         unavailable if it is coded with non-ALWIP intra modes when         constructing the MPM list for the current block with ALWIP mode.         -   a. Alternatively, a neighboring block is treated as being             coded with a predefined ALWIP intra-prediction mode X if it             is coded with non-ALWIP intra modes when constructing the             MPM list for the current block with ALWIP mode.             -   i. In one example, X may depend on the block dimensions,                 such as width and/or height.     -   7. It is proposed to remove the storage of ALWIP flag from line         buffer.         -   a. In one example, when the 2^(nd) block to be accessed is             located in a different LCU/CTU row/region compared to the             current block, the conditional check of whether the 2^(nd)             block is coded with ALWIP is skipped.         -   b. In one example, when the 2^(nd) block to be accessed is             located in a different LCU/CTU row/region compared to the             current block, the 2^(nd) block is treated in the same way             as non-ALWIP mode, such as treated as normal intra coded             block.     -   8. When encoding the ALWIP flag, no more than K (K>=0) contexts         may be used.         -   a. In one example, K=1.     -   9. It is proposed to store the converted intra prediction mode         of ALWIP coded blocks instead of directly storing the mode index         associated with the ALWIP mode.         -   a. In one example, the decoded mode index associated with             one ALWIP coded block is mapped to the normal intra mode,             such as according to map_alwip_to_angular as described in             Section 2.5.7.         -   b. Alternatively, furthermore, the storage of ALWIP flag is             totally removed.         -   c. Alternatively, furthermore, the storage of ALWIP mode is             totally removed.         -   d. Alternatively, furthermore, condition check of whether             one neighboring/current block is coded with ALWIP flag may             be skipped.         -   e. Alternatively, furthermore, the conversion of modes             assigned for ALWIP coded blocks and normal intra predictions             associated with one accessed block may be skipped.

ALWIP on Different Color Components

-   -   10. It is proposed that an inferred chroma intra mode (e.g., DM         mode) might be always applied if the corresponding luma block is         coded with ALWIP mode.         -   a. In one example, chroma intra mode is inferred to be DM             mode without signaling if the corresponding luma block is             coded with ALWIP mode.         -   b. In one example, the corresponding luma block may be the             one covering the corresponding sample of a chroma sample             located at a given position (e.g., top-left of current             chroma block, center of current chroma block).         -   c. In one example, the DM mode may be derived according to             the intra prediction mode of the corresponding luma block,             such as via mapping the (ALWIP) mode to one of the normal             intra mode.     -   11. When the corresponding luma block of the chroma blocks is         coded with ALWIP mode, several DM modes may be derived.     -   12. It is proposed that a special mode is assigned to the chroma         blocks if one corresponding luma block is coded with ALWIP mode.         -   a. In one example, the special mode is defined to be a given             normal intra prediction mode regardless the intra prediction             mode associated with the ALWIP coded blocks.         -   b. In one example, different ways of intra prediction may be             assigned to this special mode.     -   13. It is proposed that ALWIP may also be applied to chroma         components.         -   a. In one example, the matrix and/or bias vector may be             different for different color components.         -   b. In one example, the matrix and/or bias vector may be             predefined jointly for Cb and Cr.             -   i. In one example, Cb and Cr component may be                 concatenated.             -   ii. In one example, Cb and Cr component may be                 interleaved.         -   c. In one example, the chroma component may share the same             ALWIP intra-prediction mode as the corresponding luma block.             -   i. In one example, the same ALWIP intra-prediction mode                 is applied on the chroma component if the corresponding                 luma block applies the ALWIP mode and the chroma block                 is coded with DM mode.             -   ii. In one example, the same ALWIP intra-prediction mode                 is applied on the chroma component and the linear                 interpolation thereafter can be skipped.             -   iii. In one example, the same ALWIP intra-prediction                 mode is applied on the chroma component with a                 subsampled matrix and/or bias vector.         -   d. In one example, the number of ALWIP intra-prediction             modes for different component may be different.             -   i. For example, the number of ALWIP intra-prediction                 modes for chroma components may be less than that for                 luma component for the same block width and height.

Applicability of ALWIP

-   -   14. It is proposed that whether ALWIP can be applied may be         signaled.         -   a. For example, it may be signaled at sequence level (e.g.             in SPS), at picture level (e.g. in PPS or picture header),             at slice level (e.g. in slice header), at tile group level             (e.g. in tile group header), at tile level, at CTU row             level, or at CTU level.         -   b. For example, intra_lwip_flag may not be signaled and             inferred to be 0 if ALWIP cannot be applied.     -   15. It is proposed that whether ALWIP can be applied may depend         on the block width (W) and/or height (H).         -   c. For example, ALWIP may not be applied if W>=T1 (or W>T1)             and H>=T2 (or H>T2). E.g. T1=T2=32;             -   i. For example, ALWIP may not be applied if W<=T1 (or                 W<T1) and H<=T2 (or H<T2). E.g. T1=T2=32;         -   d. For example, ALWIP may not be applied if W>=T1 (or W>T1)             or H>=T2 (or H>T2). E.g. T1=T2=32;             -   i. For example, ALWIP may not be applied if W<=T1 (or                 W<T1) or H<=T2 (or H<T2). E.g. T1=T2=32, or T1=T2=8;         -   e. For example, ALWIP may not be applied if W+H>=T (or             W*H>T). E.g. T=256;             -   i. For example, ALWIP may not be applied if W+H<=T (or                 W+H<T). E.g. T=256;         -   f. For example, ALWIP may not be applied if W*H>=T (or             W*H>T). E.g. T=256;             -   i. For example, ALWIP may not be applied if W*H<=T (or                 W*H<T). E.g. T=256;         -   g. For example, intra_lwip_flag may not be signaled and             inferred to be 0 if ALWIP cannot be applied.

Calculation Problems in ALWIP

-   -   16. It is proposed that any shift operation involved in ALWIP         can only left shift or right shift a number by S, where S must         be larger or equal to 0.         -   a. In one example, the right shift operation may be             different when S is equal to 0 or larger than 0.             -   i. In one example, upsBdryX[x] should be calculated as                 upsBdryX[x]=(Σ_(i=0) ^(uDwn-1)                 RefX[x*uDwn+i]+(1<<(Log2(uDwn)−1)))>>Log2(uDwn) when                 uDwn>1, and upsBdryX[x]=(Σ_(i=0) ^(uDwn-1)                 RefX[x*uDwn+i] when uDwn is equal to 1.         -   b. In one example, upsBdryX[x] should be calculated as             upsBdryX[x]=(Σ_(i=0) ^(uDwn-1)             RefX[x*uDwn+i]+(1<<Log2(uDwn)>>1))>>Log2(uDwn)     -   17. It is proposed that the results should be rounded         toward-zero or away-from-zero in the up-sampling process of         ALWIP.         -   a. In one example,

predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor  (8-X39)

and

predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer  (8-X40)

-   -   where offsetHor and offsetVer are integers. For example,         offsetHor=upHor/2 and offsetVer=upVer/2.         Interaction with Other Coding Tools     -   18. It is proposed that ALWIP may be used for a CIIP-coded         block.         -   a. In one example, in a CIIP-coded block, it may be             explicitly signaled whether an ALWIP intra-prediction mode             or a normal intra prediction mode such as Planar is used to             generate the intra prediction signal.         -   b. In one example, it may be implicitly inferred whether an             ALWIP intra-prediction mode or a normal intra prediction             mode such as Planar may be used to generate the intra             prediction signal.             -   i. In one example, ALWIP intra-prediction mode may never                 be used in a CIIP coded block.                 -   1) Alternatively, normal intra prediction may never                     be used in a CIIP coded block.             -   ii. In one example, it may be inferred from information                 of neighboring blocks whether an ALWIP intra-prediction                 mode or a normal intra prediction mode such as Planar is                 used to generate the intra prediction signal.     -   19. It is proposed that the whole or partial of the procedure         used to down-sample the neighboring luma samples in the CCLM         mode may be used to down-sample the neighboring samples in the         ALWIP mode.         -   a. Alternatively, the whole or partial of the procedure used             to down-sample the neighboring luma samples in the ALWIP             mode may be used to down-sample the neighboring samples in             the CCLM mode.         -   b. The down-sampling procedure may be invoked with different             parameters/arguments when it is used in the CCLM process and             ALWIP process.         -   c. In one example, the down-sampling method (such as             selection of neighboring luma locations, down-sampling             filters) in the CCLM process may be utilized in the ALWIP             process.         -   d. The procedure used to down-sample the neighboring luma             samples at least include the selection of down-sampled             positions, the down-sampling filters, the rounding and             clipping operations.     -   20. It is proposed that a block coded with ALWIP mode cannot         apply RST or/and secondary transform or/and rotation transform         or/and Non-Separable Secondary Transform (NSST).         -   a. In one example, whether such constraint may be applied or             not may depend on the dimension information of the block,             e.g., same as conditions described in (15).         -   b. Alternatively, ALWIP mode may be disallowed when RST             or/and secondary transform or/and rotation transform or/and             NSST is applied.         -   c. Alternatively, a block coded with ALWIP mode may apply             RST or/and secondary transform or/and rotation transform             or/and Non-Separable Secondary Transform (NSST).             -   i. In one example, the selection of transform matrix may                 depend the ALWIP intra-prediction mode.             -   ii. In one example, the selection of transform matrix                 may depend the normal intra-prediction mode which is                 converted from the ALWIP intra-prediction mode.             -   iii. In one example, the selection of transform matrix                 may depend the classification on the normal                 intra-prediction mode which is converted from the ALWIP                 intra-prediction mode.     -   21. It is proposed that a block coded with ALWIP mode cannot         apply Block-based DPCM (BDPCM) or Residue RDPCM.         -   a. Alternatively, ALWIP mode may be disallowed when BDPCM or             RDPCM is applied.     -   22. It is proposed that a block coded with ALWIP mode may only         use DCT-II as the transform.         -   a. In one example, the signalling of transform matrix             indices is always skipped.         -   b. Alternatively, it is proposed that the transform used for             a block coded with ALWIP mode may be implicitly derived             instead of explicitly signaled. For example, the transform             may be selected following the way proposed in JVET-M0303.         -   c. Alternatively, it is proposed that a block coded with             ALWIP mode may only use transform skip.             -   i. Alternatively, furthermore, when ALWIP is used, the                 signalling of indication of usage of transform skip is                 skipped.         -   d. In one example, ALWIP mode information (such as             enabled/disabled, prediction mode index) may be             conditionally signalled after indications of transform             matrix.             -   i. In one example, for a given transform matrix (such as                 transform skip or DCT-II), the indications of ALWIP mode                 information may be signalled.             -   ii. Alternatively, furthermore, the indications of ALWIP                 mode information may be skipped for some pre-defined                 transform matrices.     -   23. It is proposed that a block coded with ALWIP mode is         regarded to be coded with a normal intra-prediction converted         from the ALWIP intra-prediction mode when the selected transform         is mode-dependent.     -   24. ALWIP mode may not use transform skip.         -   a. For example, there is no need to further signal the             indication of usage of transform skip in this case.         -   b. Alternatively, ALWIP mode may be disallowed when             transform skip is applied.             -   i. For example, there is no need to signal ALWIP mode                 information when transform skip is applied in this case.     -   25. In the filtering process, such as deblocking filter, sample         adaptive offset (SAO), adaptive loop filter (ALF), how to select         the filters and/or whether to filter samples may be determined         by the usage of ALWIP.     -   26. Unfiltered neighboring samples may be used in ALWIP mode.         -   a. Alternatively, filtered neighboring samples may be used             in ALWIP mode.         -   b. In one example, filtered neighboring samples may be used             for down sampling and unfiltered neighboring samples may be             used for up sampling.         -   c. In one example, unfiltered neighboring samples may be             used for down sampling and filtered neighboring samples may             be used for up sampling.         -   d. In one example, filtered left neighboring samples may be             used in up sampling and unfiltered above neighboring samples             may be used in up sampling.         -   e. In one example, unfiltered left neighboring samples may             be used in up sampling and filtered above neighboring             samples may be used in up sampling.         -   f. In one example, whether filter or unfiltered neighboring             samples is used may depend on the ALWIP mode.             -   i. In one example, ALWIP mode may be converted to                 traditional intra prediction mode, and whether filtered                 or unfiltered neighboring samples is used may depend on                 the converted traditional intra prediction mode. For                 example, such decision is same as traditional intra                 prediction modes.             -   ii. Alternatively, whether filter or unfiltered                 neighboring samples is used for ALWIP mode may be                 signaled.         -   g. In one example, the filtered samples may be generated             same as traditional intra prediction modes.     -   27. Which matrices or/and offset vectors are used may depend on         reshaping (a.k.a. LMCS, luma mapping with chroma scaling)         information.         -   a. In one example, different matrices or/and offset vectors             may be used when reshaping is on and off.         -   b. In one example, different matrices or/and offset vectors             may be used for different reshaping parameters.         -   c. In one example, ALWIP may be always performed in original             domain.             -   i. For example, neighboring sample are mapped to the                 original domain (if reshaping is applied) before used in                 ALWIP.     -   28. ALWIP may be disabled when reshaping is applied.         -   a. Alternatively, reshaping may be disabled when ALWIP is             enabled.         -   b. In one example, ALWIP may be disabled for HDR (high             dynamic range) content when reshaping is applied.     -   29. The matrices used in ALWIP may depend on sample bit-depth.     -   30. It is proposed that the prediction generated by ALWIP may be         treated as an intermediate signal which will be processed to         obtain the prediction signal to be further used.         -   a. In one example, Position Dependent Intra Prediction             Combination (PDPC) may be applied on the prediction             generated by ALWIP to generate the prediction signal to be             further used.         -   b. In one example, the boundary samples prediction generated             by ALWIP may be filtered with neighbouring samples to             generate the prediction signal to be further used.     -   31. It is proposed that interpolation filters other than         bilinear interpolation filter may be used in the up-sampling         process of ALWIP.         -   a. In one example, 4-tap interpolation filters may be used             in the up-sampling process of ALWIP.             -   i. For example, the 4-tap interpolation filters in VVC                 used to do the motion compensation for chroma components                 may be used in the up-sampling process of ALWIP.             -   ii. For example, the 4-tap interpolation filters in VVC                 used to do angular intra-prediction may be used in the                 up-sampling process of ALWIP.             -   iii. For example, the 8-tap interpolation filters in VVC                 used to do the motion compensation for luma component                 may be used in the up-sampling process of ALWIP.

The examples described above may be incorporated in the context of the methods described below, e.g., methods 1100 to 1400, and 2000 to 3800, which may be implemented at a video encoder and/or decoder.

FIG. 11 shows a flowchart of an exemplary method for video processing. The method 1100 includes, at step 1102, determining that a current video block is coded using an affine linear weighted intra prediction (ALWIP) mode.

The method 1100 includes, at step 1104, constructing, based on the determining, at least a portion of a most probable mode (MPM) list for the ALWIP mode based on an at least a portion of an MPM list for a non-ALWIP intra mode.

The method 1100 includes, at step 1106, performing, based on the MPM list for the ALWIP mode, a conversion between the current video block and a bitstream representation of the current video block.

In some embodiments, a size of the MPM list of the ALWIP mode is identical to a size of the MPM list for the non-ALWIP intra mode. In an example, the size of the MPM list of the ALWIP mode is 6.

In some embodiments, the method 1100 further comprises the step of inserting default modes to the MPM list for the ALWIP mode. In an example, the default modes are inserted prior to the portion of a MPM list for the ALWIP mode that is based on the MPM list for the non-ALWIP intra mode. In another example, the default modes are inserted subsequent to the portion of a MPM list for the ALWIP mode that is based on the MPM list for the non-ALWIP intra mode. In yet another example, the default modes are inserted in an interleaved manner with the portion of a MPM list for the ALWIP mode that is based on the MPM list for the non-ALWIP intra mode.

In some embodiments, constructing the MPM list for the ALWIP mode and the MPM list for the non-ALWIP intra mode is based on one or more neighboring blocks.

In some embodiments, constructing the MPM list for the ALWIP mode and the MPM list for the non-ALWIP intra mode is based a height or a width of the current video block.

In some embodiments, constructing the MPM list for the ALWIP mode is based on a first set of parameters that is different from a second set of parameters used to construct the MPM list for the non-ALWIP intra mode.

In some embodiments, the method 1100 further includes the step of determining that a neighboring block of the current video block has been coded with the ALWIP mode, and designating, in constructing the MPM list for the non-ALWIP intra mode, the neighboring block as unavailable.

In some embodiments, the method 1100 further includes the step of determining that a neighboring block of the current video block has been coded with the non-ALWIP intra mode, and designating, in constructing the MPM list for the ALWIP mode, the neighboring block as unavailable.

In some embodiments, the non-ALWIP intra mode is based on a normal intra mode, a multiple reference line (MRL) intra prediction mode or an intra sub-partition (ISP) tool.

FIG. 12 shows a flowchart of an exemplary method for video processing. The method 1200 includes, at step 1210, determining that a luma component of a current video block is coded using an affine linear weighted intra prediction (ALWIP) mode.

The method 1200 includes, at step 1220, inferring, based on the determining, a chroma intra mode.

The method 1200 includes, at step 1230, performing, based on the chroma intra mode, a conversion between the current video block and a bitstream representation of the current video block.

In some embodiments, the luma component covers a predetermined chroma sample of the chroma component. In an example, the predetermined chroma sample is a top-left sample or a center sample of the chroma component.

In some embodiments, the inferred chroma intra mode is a DM mode.

In some embodiments, the inferred chroma intra mode is the ALWIP mode.

In some embodiments, the ALWIP mode is applied to one or more chroma components of the current video block.

In some embodiments, different matrix or bias vectors of the ALWIP mode are applied to different color components of the current video block. In an example, the different matrix or bias vectors are predefined jointly for Cb and Cr components. In another example, the Cb and Cr components are concatenated. In yet another example, the Cb and Cr components are interleaved.

FIG. 13 shows a flowchart of an exemplary method for video processing. The method 1300 includes, at step 1302, determining that a current video block is coded using an affine linear weighted intra prediction (ALWIP) mode.

The method 1300 includes, at step 1304, performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block.

In some embodiments, the determining is based on signaling in a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, a tile group header, a tile header, a coding tree unit (CTU) row or a CTU region.

In some embodiments, the determining is based on a height (H) or a width (W) of the current video block. In an example, W>T1 or H>T2. In another example, W≥T1 or H≥T2. In yet another example, W<T1 or H<T2. In yet another example, W≤T1 or H≤T2. In yet another example, T1=32 and T2=32.

In some embodiments, the determining is based on a height (H) or a width (W) of the current video block. In an example, W+H≤T. In another example, W+H≥T. In yet another example, W×H≤T. In yet another example, W×H≥T. In yet another example, T=256.

FIG. 14 shows a flowchart of an exemplary method for video processing. The method 1400 includes, at step 1402, determining that a current video block is coded using a coding mode different from an affine linear weighted intra prediction (ALWIP) mode.

The method 1400 includes, at step 1404, performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block.

In some embodiments, the coding mode is a combined intra and inter prediction (CIIP) mode, and method 1400 further includes the step of performing a selection between the ALWIP mode and a normal intra prediction mode. In an example, performing the selection is based on an explicit signaling in the bitstream representation of the current video block. In another example, performing the selection is based on predetermined rule. In yet another example, the predetermined rule always selects the ALWIP mode when the current video block is coded using the CIIP mode. In yet another example, the predetermined rule always selects the normal intra prediction mode when the current video block is coded using the CIIP mode.

In some embodiments, the coding mode is a cross-component linear model (CCLM) prediction mode. In an example, a downsampling procedure for the ALWIP mode is based on a downsampling procedure for the CCLM prediction mode. In another example, the downsampling procedure for the ALWIP mode is based on a first set of parameters, and where the downsampling procedure for the CCLM prediction mode is based on a second set of parameters different from the first set of parameters. In yet another example, the downsampling procedure for the ALWIP mode or the CCLM prediction mode comprises at least one of a selection of downsampled positions, a selection of downsampling filters, a rounding operation or a clipping operation.

In some embodiments, the method 1400 further includes the step of applying one or more of a Reduced Secondary Transform (RST), a secondary transform, a rotation transform or a Non-Separable Secondary Transform (NSST).

In some embodiments, the method 1400 further includes the step of applying block-based differential pulse coded modulation (DPCM) or residual DPCM.

6 Example Implementations of the Disclosed Technology

FIG. 15 is a block diagram of a video processing apparatus 1500. The apparatus 1500 may be used to implement one or more of the methods described herein. The apparatus 1500 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus 1500 may include one or more processors 1502, one or more memories 1504 and video processing hardware 1506. The processor(s) 1502 may be configured to implement one or more methods (including, but not limited to, methods 1100 to 1400, and 2000 to 3800) described in the present document. The memory (memories) 1504 may be used for storing data and code used for implementing the methods and techniques described herein. The video processing hardware 1506 may be used to implement, in hardware circuitry, some techniques described in the present document.

In some embodiments, the video coding methods may be implemented using an apparatus that is implemented on a hardware platform as described with respect to FIG. 15.

FIG. 16 is a block diagram showing an example video processing system 1600 in which various techniques disclosed herein may be implemented. Various implementations may include some or all of the components of the system 1600. The system 1600 may include input 1602 for receiving video content. The video content may be received in a raw or uncompressed format, e.g., 8 or 10 bit multi-component pixel values, or may be in a compressed or encoded format. The input 1602 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON), etc. and wireless interfaces such as Wi-Fi or cellular interfaces.

The system 1600 may include a coding component 1604 that may implement the various coding or encoding methods described in the present document. The coding component 1604 may reduce the average bitrate of video from the input 1602 to the output of the coding component 1604 to produce a coded representation of the video. The coding techniques are therefore sometimes called video compression or video transcoding techniques. The output of the coding component 1604 may be either stored, or transmitted via a communication connected, as represented by the component 1606. The stored or communicated bitstream (or coded) representation of the video received at the input 1602 may be used by the component 1608 for generating pixel values or displayable video that is sent to a display interface 1610. The process of generating user-viewable video from the bitstream representation is sometimes called video decompression. Furthermore, while certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or Displayport, and so on. Examples of storage interfaces include SATA (serial advanced technology attachment), PCI, IDE interface, and the like. The techniques described in the present document may be embodied in various electronic devices such as mobile phones, laptops, smartphones or other devices that are capable of performing digital data processing and/or video display.

Some embodiments of the disclosed technology include making a decision or determination to enable a video processing tool or mode. In an example, when the video processing tool or mode is enabled, the encoder will use or implement the tool or mode in the processing of a block of video, but may not necessarily modify the resulting bitstream based on the usage of the tool or mode. That is, a conversion from the block of video to the bitstream representation of the video will use the video processing tool or mode when it is enabled based on the decision or determination. In another example, when the video processing tool or mode is enabled, the decoder will process the bitstream with the knowledge that the bitstream has been modified based on the video processing tool or mode. That is, a conversion from the bitstream representation of the video to the block of video will be performed using the video processing tool or mode that was enabled based on the decision or determination.

Some embodiments of the disclosed technology include making a decision or determination to disable a video processing tool or mode. In an example, when the video processing tool or mode is disabled, the encoder will not use the tool or mode in the conversion of the block of video to the bitstream representation of the video. In another example, when the video processing tool or mode is disabled, the decoder will process the bitstream with the knowledge that the bitstream has not been modified using the video processing tool or mode that was disabled based on the decision or determination.

FIG. 17 is a block diagram that illustrates an example video coding system 100 that may utilize the techniques of this disclosure. As shown in FIG. 17, video coding system 100 may include a source device 110 and a destination device 120. Source device 110 generates encoded video data which may be referred to as a video encoding device. Destination device 120 may decode the encoded video data generated by source device 110 which may be referred to as a video decoding device. Source device 110 may include a video source 112, a video encoder 114, and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures. Video encoder 114 encodes the video data from video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. I/O interface 116 may include a modulator/demodulator (modem) and/or a transmitter. The encoded video data may be transmitted directly to destination device 120 via I/O interface 116 through network 130 a. The encoded video data may also be stored onto a storage medium/server 130 b for access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/server 130 b. Video decoder 124 may decode the encoded video data. Display device 122 may display the decoded video data to a user. Display device 122 may be integrated with the destination device 120, or may be external to destination device 120 which be configured to interface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding (VVM) standard and other current and/or further standards.

FIG. 18 is a block diagram illustrating an example of video encoder 200, which may be video encoder 114 in the system 100 illustrated in FIG. 17.

Video encoder 200 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 18, video encoder 200 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of video encoder 200. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partition unit 201, a predication unit 202 which may include a mode select unit 203, a motion estimation unit 204, a motion compensation unit 205 and an intra prediction unit 206, a residual generation unit 207, a transform unit 208, a quantization unit 209, an inverse quantization unit 210, an inverse transform unit 211, a reconstruction unit 212, a buffer 213, and an entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, or different functional components. In an example, predication unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform predication in an IBC mode in which at least one reference picture is a picture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 and motion compensation unit 205 may be highly integrated but are represented in the example of FIG. 18 separately for purposes of explanation.

Partition unit 201 may partition a picture into one or more video blocks. Video encoder 200 and video decoder 300 may support various video block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra- or inter-coded block to a residual generation unit 207 to generate residual block data and to a reconstruction unit 212 to reconstruct the encoded block for use as a reference picture. In some example, Mode select unit 203 may select a combination of intra and inter predication (CIIP) mode in which the predication is based on an inter predication signal and an intra predication signal. Mode select unit 203 may also select a resolution for a motion vector (e.g., a sub-pixel or integer pixel precision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimation unit 204 may generate motion information for the current video block by comparing one or more reference frames from buffer 213 to the current video block. Motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from buffer 213 other than the picture associated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may perform different operations for a current video block, for example, depending on whether the current video block is in an I slice, a P slice, or a B slice.

In some examples, motion estimation unit 204 may perform uni-directional prediction for the current video block, and motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. Motion estimation unit 204 may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. Motion estimation unit 204 may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block.

In other examples, motion estimation unit 204 may perform bi-directional prediction for the current video block, motion estimation unit 204 may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. Motion estimation unit 204 may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. Motion estimation unit 204 may output the reference indexes and the motion vectors of the current video block as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video blocks indicated by the motion information of the current video block.

In some examples, motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a full set of motion information for the current video. Rather, motion estimation unit 204 may signal the motion information of the current video block with reference to the motion information of another video block. For example, motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder 300 that the current video block has the same motion information as another video block.

In another example, motion estimation unit 204 may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD). The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.

As discussed above, video encoder 200 may predictively signal the motion vector. Two examples of predictive signaling techniques that may be implemented by video encoder 200 include advanced motion vector predication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the current video block. When intra prediction unit 206 performs intra prediction on the current video block, intra prediction unit 206 may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include a predicted video block and various syntax elements.

Residual generation unit 207 may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block(s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block.

In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and residual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block.

After transform processing unit 208 generates a transform coefficient video block associated with the current video block, quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. Reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the predication unit 202 to produce a reconstructed video block associated with the current block for storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed reduce video blocking artifacts in the video block.

Entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When entropy encoding unit 214 receives the data, entropy encoding unit 214 may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data.

FIG. 19 is a block diagram illustrating an example of video decoder 300 which may be video decoder 114 in the system 100 illustrated in FIG. 17.

The video decoder 300 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 19, the video decoder 300 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video decoder 300. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

In the example of FIG. 19, video decoder 300 includes an entropy decoding unit 301, a motion compensation unit 302, an intra prediction unit 303, an inverse quantization unit 304, an inverse transformation unit 305, and a reconstruction unit 306 and a buffer 307. Video decoder 300 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 200 (FIG. 18).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data). Entropy decoding unit 301 may decode the entropy coded video data, and from the entropy decoded video data, motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. Motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used by video encoder 20 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. Motion compensation unit 302 may determine the interpolation filters used by video encoder 200 according to received syntax information and use the interpolation filters to produce predictive blocks.

Motion compensation unit 302 may uses some of the syntax information to determine sizes of blocks used to encode frame(s) and/or slice(s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. Inverse quantization unit 303 inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. Inverse transform unit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit 202 or intra-prediction unit 303 to form decoded blocks. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decoded video blocks are then stored in buffer 307, which provides reference blocks for subsequent motion compensation/intra predication and also produces decoded video for presentation on a display device.

In some embodiments, the ALWIP mode or the MIP mode is used to compute a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation (or an averaging operation), followed by a matrix vector multiplication operation, and selectively (or optionally) followed by an upsampling operation (or a linear interpolation operation). In some embodiments, the ALWIP mode or the MIP mode is used to compute a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation (or an averaging operation) and followed by a matrix vector multiplication operation. In some embodiments, the ALWIP mode or the MIP mode can also perform an upsampling operation (or a linear interpolation operation) after performing the matrix vector multiplication operation.

FIG. 20 shows an example flowchart of an example method 2000 for matrix-based intra prediction. Operation 2002 includes generating, for a conversion between a current video block of a video and a coded representation of the current video block, a first most probable mode (MPM) list using a first procedure based on a rule. Operation 2004 includes performing the conversion between the current video block and the coded representation of the current video block using the first MPM list, where the conversion of the current video block uses a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where the rule specifies that the first procedure used for generation of the first MPM list is same as a second procedure used for generation of a second MPM list for conversion of other video blocks of the video that are coded using a non-MIP intra mode that is different from the MIP mode, and where at least a portion of the first MPM list is generated based on at least a portion of the second MPM list.

In some embodiments for method 2000, a size of the first MPM list for the MIP mode is same as that of the second MPM list for the non-MIP intra mode. In some embodiments for method 2000, the size of the first MPM list for the MIP mode and of the second MPM list for the non-MIP intra mode is 6. In some embodiments for method 2000, the second MPM list for the non-MIP intra mode is constructed before the first MPM list for the MIP mode is constructed. In some embodiments for method 2000, the portion or all of the second MPM list for the non-MIP intra mode is converted to MPMs that are added to the portion of the first MPM list for the MIP mode.

In some embodiments for method 2000, a subset of the MPMs are added to the portion of the first MPM list for the MIP mode by pruning the MPMs. In some embodiments, the method 2000 further includes adding default intra-prediction modes to the first MPM list for the MIP mode. In some embodiments for method 2000, the default intra-prediction modes are added to the first MPM list for the MIP mode prior to the portion of the first MPM list for the MIP mode that is based on the portion of the second MPM list for the non-MIP intra mode. In some embodiments for method 2000, the default intra-prediction modes are added to the first MPM list for the MIP mode after the portion of the first MPM list for the MIP mode that is based on the portion of the second MPM list for the non-MIP intra mode. In some embodiments for method 2000, the default intra-prediction modes are added to the first MPM list for the MIP mode in an interleaved manner with the portion of the first MPM list for the MIP mode that is based on the portion of the second MPM list for the non-MIP intra mode. In some embodiments for method 2000, the default intra-prediction modes are same for a plurality of types of video blocks. In some embodiments for method 2000, the default intra-prediction modes are determined based on coded information of the current video block. In some embodiments for method 2000, the coded information includes availability of neighboring video blocks, mode information of the neighboring video blocks, or block dimension of the current video block.

In some embodiments for method 2000, one intra-prediction mode in the second MPM list for the non-MIP intra mode is converted to its corresponding MIP mode to obtain a converted MIP mode that is added to the first MPM list for the MIP mode. In some embodiments for method 2000, all intra-prediction modes in the second MPM list for the non-MIP intra mode are converted to its corresponding MIP mode to obtain a plurality of converted MIP modes that are added to the first MPM list for the MIP mode. In some embodiments for method 2000, all intra-prediction modes are converted to its corresponding MIP mode to obtain a plurality of converted MIP modes that are used to construct the second MPM list for the non-MIP intra mode. In some embodiments for method 2000, the all intra-prediction modes include intra-prediction modes from neighboring video blocks of the current video block and default intra-prediction modes. In some embodiments for method 2000, the default intra-prediction modes include a planar mode and a direct current (DC) mode.

In some embodiments for method 2000, two intra-prediction modes in the second MPM list for the non-MIP intra mode are converted to its corresponding MIP modes to obtain two converted MIP modes, and one of two converted MIP modes is added to the first MPM list for the MIP mode in response to the two converted MIP modes being same. In some embodiments for method 2000, two intra-prediction modes in the second MPM list for the non-MIP intra mode are converted to its corresponding MIP modes to obtain two converted MIP modes, and one of two converted MIP modes is added to the second MPM list for the non-MIP intra mode in response to the two converted MIP modes being same. In some embodiments for method 2000, the second MPM list for non-MIP intra mode includes S intra-prediction modes, and where K out of S intra-prediction modes is or are selected to be included in the first MPM list for MIP mode. In some embodiments for method 2000, K is 3 and S is 6. In some embodiments for method 2000, the first K intra-prediction modes in the second MPM list for non-MIP intra mode is selected to be included in the first MPM list for MIP mode. In some embodiments for method 2000, the first MPM list for the MIP mode and the second MPM list for the non-MIP intra mode is derived or constructed based on one or more neighboring video blocks of the current video block. In some embodiments for method 2000, the first MPM list for the MIP mode and the second MPM list for the non-MIP intra mode is derived or constructed based on a same neighboring video block located to a left of the current video block.

In some embodiments for method 2000, the same neighboring video block located to the left is directly to left of the current video block and is aligned with the current video block. In some embodiments for method 2000, the same neighboring video block located to the left and below the current video block. In some embodiments for method 2000, the first MPM list for the MIP mode and the second MPM list for the non-MIP intra mode is derived or constructed based on a same neighboring video block, where the same neighboring video block is located to left of the current video block at a bottom-most position or the same neighboring video block is located above the current video block at a right-most position. In some embodiments for method 2000, the first MPM list for the MIP mode and the second MPM list for the non-MIP intra mode is derived or constructed based on a same neighboring video block located above the current video block.

In some embodiments for method 2000, the same neighboring video block located to above is directly above the current video block and is aligned with the current video block. In some embodiments for method 2000, the same neighboring video block located to left and above the current video block. In some embodiments for method 2000, the first MPM list for the MIP mode and the second MPM list for the non-MIP intra mode is derived or constructed based on a same neighboring video block, where the same neighboring video block is located above the current video block at a left-most position or the same neighboring video block is located to left of the current video block at a top-most position. In some embodiments for method 2000, the non-MIP intra mode is based on an intra prediction mode, a multiple reference line (MRL) intra prediction mode, or an intra sub-partition (ISP) tool. In some embodiments for method 2000, the first MPM list for the MIP mode is further based on a height or a width of the current video block.

In some embodiments for method 2000, the first MPM list for the MIP mode is further based on a height or a width of a neighboring video block of the current video block. In some embodiments for method 2000, the first MPM list for the MIP mode is constructed based on a first set of parameters that is different from a second set of parameters used to construct the second MPM list for the non-MIP intra mode. In some embodiments for method 2000, the second MPM list for non-MIP intra mode includes S intra-prediction modes, and where K out of S intra-prediction modes are derived to be included in the first MPM list for MIP mode. In some embodiments for method 2000, K is 3 and S is 6.

In some embodiments for method 2000, the first K intra-prediction modes in the second MPM list for non-MIP intra mode is derived to be included in the first MPM list for MIP mode. In some embodiments for method 2000, a first mode listed in the first MPM list for MIP mode is different from a first mode listed in the second MPM list for non-MIP intra mode. In some embodiments for method 2000, the first mode listed in the first MPM list for MIP mode is a first mode, and where the first mode listed in the second MPM list for non-MIP intra mode is a planar mode. In some embodiments for method 2000, the first mode in the first MPM list for MIP mode is converted from the planar mode in the second MPM list for non-MIP intra mode.

In some embodiments for method 2000, the first MPM list for MIP mode includes a first set of stuffing modes that are different from a second set of stuffing modes included in the second MPM list for non-MIP intra mode. In some embodiments for method 2000, the first set of stuffing modes include a first mode, a second mode, and a third mode, and where the second set of stuffing modes include a direct current (DC) mode, a vertical mode, and a horizontal mode. In some embodiments for method 2000, the first mode, the second mode, and the third mode are included in the first set of stuffing modes based on a size of the current video block. In some embodiments for method 2000, the first MPM list for MIP mode includes a first set of intra-prediction modes of neighboring video blocks of the current video block, the second MPM list for non-MIP intra mode includes a second set of intra-prediction modes of the neighboring video blocks of the current video block, and the first set of intra-prediction modes are different from the second set of intra-prediction modes.

In some embodiments for method 2000, the second set of intra-prediction modes include intra-prediction modes that are converted to MIP modes that are included in the first set of intra-prediction modes. In some embodiments for method 2000, the first MPM list for MIP mode includes a first set of shifted intra-prediction modes, the second MPM list for non-MIP intra mode includes a second set of shifted intra-prediction modes, and the first set of shifted intra-prediction modes are different from the second set of shifted intra-prediction modes. In some embodiments for method 2000, the first set of shifted intra-prediction modes includes an MIP mode (Y) shifted by K1 according to a first formula Y+K1, the second set of shifted intra-prediction modes includes a non-MIP intra mode (X) shifted by K0 according to a second formula X+K0, and K1 is different from K0. In some embodiments for method 2000, K1 depends on a width and a height of the current video block.

In some embodiments, the method 2000 further includes performing a first determination that a neighboring video block of the current video block is coded with a non-MIP intra mode; and performing a second determination, in response to the first determination, that the neighboring video block is unavailable for the constructing of the first MPM list for the MIP mode.

In some embodiments, the method 2000 further includes performing a first determination that a neighboring video block of the current video block is coded with a non-MIP intra mode; and performing, in response to the first determination, a second determination that the neighboring video block is coded with a pre-defined MIP intra-prediction mode, where the first MPM list for the MIP mode is constructed using the pre-defined MIP intra-prediction mode. In some embodiments for method 2000, the pre-defined MIP intra-prediction mode depends on a width and/or a height of the current video block.

FIG. 21 shows an example flowchart of an example method 2100 for matrix-based intra prediction. Operation 2100 includes generating, for a conversion between a current video block of a video and a coded representation of the current video block, a most probable mode (MPM) list based on a rule, where the rule is based on whether a neighboring video block of the current video block is coded with a matrix based intra prediction (MIP) mode in which a prediction block of the neighboring video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2104 includes performing the conversion between the current video block and the coded representation of the current video block using the MPM list, where the conversion applies a non-MIP mode to the current video block, and where the non-MIP mode is different from the MIP mode.

In some embodiments for method 2100, the rule specifies that the neighboring video block coded with the MIP mode is treated as unavailable for generating the MPM list for the non-MIP coded current video block. In some embodiments for method 2100, the rule specifies that the neighboring video block coded with the MIP mode is determined to be coded with a pre-defined intra-prediction mode. In some embodiments for method 2100, the rule specifies that the pre-defined intra-prediction mode includes a planar mode.

FIG. 22 shows an example flowchart of an example method 2200 for matrix-based intra prediction. Operation 2202 includes decoding a current video block of a video that is coded in a coded representation of the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2204 includes updating a line buffer associated with the decoding without storing in the line buffer information indicating whether the current video block is coded using the MIP mode.

In some embodiments, the method 2200 further includes accessing a second video block of the video, where the second video block is decoded before the decoding the current video block, where the second video block is located at a different Largest Coding Unit (LCU) or Coding Tree Unit (CTU) row or CTU region compared to that of the current video block, and where the current video block is decoded without determining whether the second video block is coded using the MIP mode. In some embodiments, the method 2200 further includes accessing a second video block by determining that the second video block is coded using a non-MIP intra mode without determining whether the second video block is coded using the MIP mode, where the second video located at a different Largest Coding Unit (LCU) or Coding Tree Unit (CTU) row or CTU region compared to that of the current video block; and decoding, based on the accessing the second video block, the current video block.

FIG. 23 shows an example flowchart of an example method 2300 for matrix-based intra prediction. Operation 2302 includes performing a conversion between a current video block and a bitstream representation of the current video block, where the current video block is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where a flag is coded in the bitstream presentation using at most K contexts in an arithmetic coding or a decoding process, where the flag indicates whether the current video block is coded using the MIP mode, and where K is greater than or equal to zero. In some embodiments for method 2300, K is 1. In some embodiments for method 2300, K is 4.

FIG. 24 shows an example flowchart of an example method 2400 for matrix-based intra prediction. Operation 2402 includes generating, for a conversion between a current video block of a video and a bitstream representation of the current video block, an intra prediction mode for the current video block coded with a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2404 includes determining a rule for storing information indicative of the intra prediction mode based on whether the current video block is coded with the MIP mode. Operation 2406 includes performing the conversion according to the rule, where the rule defines that a syntax element for the intra prediction mode is stored in the bitstream representation for the current video block, and where the rule defines that a mode index for the MIP mode for the current video block is not stored in the bitstream representation.

In some embodiments for method 2400, the mode index for the MIP mode is associated with the intra prediction mode. In some embodiments for method 2400, the rule defines that the bitstream representation excludes a flag that indicates that the current video block is coded with the MIP mode. In some embodiments for method 2400, the rule defines that the bitstream representation excludes a storage of information indicative of the MIP mode associated with the current video block. In some embodiments, the method 2400 further includes performing, after the conversion, a second conversion between a second video block of the video and the bitstream representation of the second video block, where the second video block is a neighboring video block of the current video block, and where the second conversion is performed without determining whether the second video block is coded using the MIP mode.

FIG. 25 shows an example flowchart of an example method 2500 for matrix-based intra prediction. Operation 2502 includes performing a first determination that a luma video block of a video is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the luma video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2504 includes performing, based on the first determination, a second determination about a chroma intra mode to be used for a chroma video block associated with the luma video block. Operation 2506 includes performing, based on the second determination, a conversion between the chroma video block and a bitstream representation of the chroma video block.

In some embodiments for method 2500, the performing the second determination includes determining that the chroma intra mode is a Derived Mode (DM) without depending on a signaling. In some embodiments for method 2500, the luma video block covers a predetermined corresponding chroma sample of the chroma video block. In some embodiments for method 2500, the predetermined corresponding chroma sample is a top-left sample or a center sample of the chroma video block. In some embodiments for method 2500, the chroma intra mode includes a Derived Mode (DM). In some embodiments for method 2500, the DM is used to derive a first intra prediction mode for the chroma video block from a second intra prediction mode of the luma video block. In some embodiments for method 2500, the MIP mode associated with the luma video block is mapped to a pre-defined intra mode.

In some embodiments for method 2500, a plurality of Derived Modes (DMs) are derived in response to the first determination that the luma video block is coded with the MIP mode. In some embodiments for method 2500, the chroma intra mode includes a specified intra prediction mode. In some embodiments for method 2500, the pre-defined intra mode or the specified intra mode is a Planar mode. In some embodiments for method 2500, the chroma video block is coded using the MIP mode. In some embodiments for method 2500, the chroma video block is coded using a first matrix or a first bias vector that are different from a second matrix or a second bias vector of a second chroma video block. In some embodiments for method 2500, the chroma video block is a blue color component, where the first matrix or the first bias vector is predefined for the blue color component, where the second chroma video block is a red color component, where the second matrix or the second bias vector is predefined for the red color component.

In some embodiments for method 2500, the blue color component and the red color component are concatenated. In some embodiments for method 2500, the blue color component and the red color component are interleaved. In some embodiments for method 2500, the chroma video block is coded using the MIP mode that is same as the MIP mode used for the luma video block. In some embodiments for method 2500, the chroma video block is coded using a Derived Mode (DM). In some embodiments for method 2500, the upsampling operation (or a linear interpolation technique) is skipped after the chroma video block is coded using the MIP mode. In some embodiments for method 2500, the chroma video block is coded using the MIP mode with a subsampled matrix and/or a bias vector. In some embodiments for method 2500, a number of MIP modes for the luma video block and the chroma video block are different. In some embodiments for method 2500, the chroma video block is associated with a first number of MIP modes, the luma video block is associated with a second number of MIP modes, and the first number of MIP modes is less than the second number of MIP modes. In some embodiments for method 2500, the chroma video block and the luma video block have a same size.

FIG. 26 shows an example flowchart of an example method 2600 for matrix-based intra prediction. Operation 2602 includes performing a conversion between a current video block of a video and a coded representation of the current video block, where the conversion is based on a determination (or based on determining) whether to code the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation.

In some embodiments of method 2600, a syntax element is included in the coded representation in response to the determination that the current video block is to be coded with the MIP mode, and the syntax element indicates the use the MIP mode for coding the current video block. In some embodiments of method 2600, the coded representation includes a syntax element that indicates that the MIP mode is enabled or disabled for the current video block, and where the syntax element indicates that the MIP mode is allowed or disallowed for coding the current video block. In some embodiments of method 2600, a syntax element is not included in the coded representation in response to the determination that the current video block is not to be coded with the MIP mode, and the syntax element indicates whether the MIP mode is used for the current video block.

In some embodiments of method 2600, a second syntax element indicating enabling of the MIP mode is further included in a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, a tile group header, a tile header, a coding tree unit (CTU) row or a CTU region. In some embodiments of method 2600, the determination whether to use the MIP mode for the conversion is based on a height (H) and/or a width (W) of the current video block. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W≥T1 and H≥T2. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W≤T1 and H≤T2. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W≥T1 or H≥T2. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W≤T1 or H≤T2. In some embodiments of method 2600, T1=32 and T2=32. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W+H≥T. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W+H≤T. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W×H≥T. In some embodiments of method 2600, the current video block is determined not to be coded using the MIP mode in response to W×H≤T. In some embodiments of method 2600, T=256.

FIG. 27A shows an example flowchart of an example video encoding method 2700A for matrix-based intra prediction. Operation 2702A includes determining, for encoding a current video block of a video into a bitstream representation of the current video block, according to a rule whether to use a matrix based intra prediction (MIP) mode and a coding mode that is different from the MIP mode for encoding the current video block, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2704A includes adding, based on the determining, an encoded representation of the current video block to the bitstream representation.

FIG. 27B shows an example flowchart of an example video decoding method 2700B for matrix-based intra prediction. Operation 2702B includes determining that a current video block of a video is encoded in a bitstream representation using a matrix based intra prediction (MIP) mode and a coding mode that is different from the MIP mode, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2704B includes generating a decoded representation of the current video block by parsing and decoding the bitstream representation.

In some embodiments for methods 2700A and/or 2700B, the coding mode is a combined intra and inter prediction (CIIP) mode, and where the method further comprises generating an intra prediction signal for the current video block by performing a selection between the MIP mode and an intra prediction mode. In some embodiments for methods 2700A and/or 2700B, the performing the selection is based on a signaling in the bitstream representation of the current video block. In some embodiments for methods 2700A and/or 2700B, the performing the selection is based on a predetermined rule. In some embodiments for methods 2700A and/or 2700B, the predetermined rule selects the MIP mode in response to the current video block being coded using the CIIP mode. In some embodiments for methods 2700A and/or 2700B, the predetermined rule selects the intra prediction mode in response to the current video block being coded using the CIIP mode. In some embodiments for method 2700A and/or 2700B, the predetermined rule selects a Planar mode in response to the current video block being coded using the CIIP mode. In some embodiments for methods 2700A and/or 2700B, the performing the selection is based on information associated with neighboring video blocks of the current video block.

In some embodiments for methods 2700A and/or 2700B, the coding mode is a cross-component linear model (CCLM) prediction mode. In some embodiments for methods 2700A and/or 2700B, a first downsampling procedure for downsampling a neighboring sample of the current video block in the MIP mode uses at least some of a second downsampling procedure for the CCLM prediction mode in which neighboring luma samples of the current video block are downsampled. In some embodiments for methods 2700A and/or 2700B, a first downsampling procedure for downsampling a neighboring sample of the current video block in the CCLM prediction mode uses at least some of a second downsampling procedure for the MIP prediction mode in which neighboring luma samples of the current video block are downsampled. In some embodiments for methods 2700A and/or 2700B, the first downsampling procedure for the MIP mode is based on a first set of parameters, and the first downsampling procedure for the CCLM prediction mode is based on a second set of parameters different from the first set of parameters.

In some embodiments for methods 2700A and/or 2700B, the first downsampling procedure for the MIP mode and the second downsampling procedure for the CCLM prediction mode include selection of neighboring luma locations or selection of downsampling filter. In some embodiments for methods 2700A and/or 2700B, the neighboring luma samples are downsampled using at least one of a selection of downsampled positions, a selection of downsampling filters, a rounding operation or a clipping operation. In some embodiments for methods 2700A and/or 2700B, the rule defines that a block-based differential pulse coded modulation (BDPCM) or a residual DPCM is not applied to the current video block coded with the MIP mode. In some embodiments for methods 2700A and/or 2700B, the rule defines that the MIP mode is disallowed for applying to the current video block in response to applying a block-based differential pulse-coded modulation (BDPCM) or a residual DPCM.

FIG. 28 shows an example flowchart of an example method 2800 for matrix-based intra prediction. Operation 2802 includes making a determination about an applicability of a loop filter to a reconstructed block of a current video block of a video in a conversion between the video and a coded representation of the current video block, where the current video block is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2804 includes processing the current video block according to the determination.

In some embodiments for method 2800, the loop filter includes a deblocking filter. In some embodiments for method 2800, the loop filter includes a sample adaptive offset (SAO). In some embodiments for method 2800, the loop filter includes an adaptive loop filter (ALF).

FIG. 29A shows an example flowchart of an example video encoding method 2900A for matrix-based intra prediction. Operation 2902A includes determining, for encoding a current video block of a video into a bitstream representation of the current video block, a type of neighboring samples of the current video block to be used according to a rule. Operation 2904A includes adding, based on the determining, an encoded representation of the current video block to the bitstream representation, where the current video block is encoded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation.

FIG. 29B shows an example flowchart of an example video decoding method 2900B for matrix-based intra prediction. Operation 2902B includes determining that a current video block of a video is encoded in a bitstream representation using a matrix based intra prediction (MIP) mode and using a type of neighboring samples of the current video block according to a rule, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 2904B includes generating a decoded representation of the current video block by parsing and decoding the bitstream representation.

In some embodiments for methods 2900A and/or 2900B, the rule defines that the type of neighboring samples are unfiltered neighboring samples. In some embodiments for methods 2900A and/or 2900B, the rule defines that the type of neighboring samples that include the unfiltered neighboring samples are used for an upsampling process, the rule defines that the type of neighboring samples that include the unfiltered neighboring samples are used for a downsampling process, and the rule defines that the type of neighboring samples that include the unfiltered neighboring samples are used for the matrix vector multiplication operation. In some embodiments for methods 2900A and/or 2900B, the rule defines that the type of neighboring samples are filtered neighboring samples. In some embodiments for methods 2900A and/or 2900B, the rule defines that the type of neighboring samples that include unfiltered neighboring samples are used for an upsampling technique, and the rule defines that the type of neighboring samples that include filtered neighboring samples are used for a downsampling technique.

In some embodiments for methods 2900A and/or 2900B, the rule defines that the type of neighboring samples that include unfiltered neighboring samples are used for a downsampling technique, and the rule defines that the type of neighboring samples that include filtered neighboring samples are used for an upsampling technique. In some embodiments for methods 2900A and/or 2900B, the rule defines that the type of neighboring samples that include unfiltered above neighboring samples are used for an upsampling technique, and the rule defines that the type of neighboring samples that include filtered left neighboring samples are used for an upsampling technique. In some embodiments for methods 2900A and/or 2900B, the rule defines that the type of neighboring samples that include unfiltered left neighboring samples are used for an upsampling technique, and the rule defines that the type of neighboring samples that include filtered above neighboring samples are used for an upsampling technique.

In some embodiments for methods 2900A and/or 2900B, the type of neighboring samples include unfiltered neighboring samples or filtered neighboring samples, and the rule defines that whether the unfiltered neighboring samples or the filtered neighboring samples are used is based on the MIP mode of the current video block.

In some embodiments, methods 2900A and/or 2900B further comprise converting the MIP mode to an intra prediction mode, where the type of neighboring samples include unfiltered neighboring samples or filtered neighboring samples, and where the rule defines that whether the unfiltered neighboring samples or the filtered neighboring samples are used is based on the intra prediction mode. In some embodiments for methods 2900A and/or 2900B, the type of neighboring samples include unfiltered neighboring samples or filtered neighboring samples, and the rule defines that whether the unfiltered neighboring samples or the filtered neighboring samples are used is based on a syntax element or signaling. In some embodiments for methods 2900A and/or 2900B, the filtered neighboring samples or the filtered left neighboring samples or the filtered above neighboring samples are generated using an intra prediction mode.

FIG. 30 shows an example flowchart of an example method 3000 for matrix-based intra prediction. Operation 3002 includes performing a conversion between a current video block of a video and a bitstream representation of the current video block, where the conversion includes generating, by using a matrix based intra prediction (MIP) mode, a prediction block for the current video block by selecting and applying matrix multiplication using matrices of samples and/or by selecting and adding an offset using offset vectors for the current video block, where the samples are obtained from a row and column wise averaging of previously coded samples of the video, and where the selecting is based on reshaping information associated with applying a luma mapping with chroma scaling (LMCS) technique on a reference picture of the current video block. In some embodiments for method 3000, when a reshaping technique is enabled for the reference picture, the reshaping information is associated with the matrices and/or the offset vectors that are different from those associated with the reshaping information when the reshaping technique is disabled for the reference picture. In some embodiments for method 3000, different matrices and/or the offset vectors are used for different reshaping parameters of the reshaping information. In some embodiments for method 3000, the performing the conversion includes performing intra prediction on the current video block using the MIP mode in an original domain. In some embodiments for method 3000, neighboring samples of the current video block are mapped to the original domain in response to applying the reshaping information, and where the neighboring samples are mapped to the original domain before being used in MIP mode.

FIG. 31 shows an example flowchart of an example method 3100 for matrix-based intra prediction. Operation 3102 includes determining that a current video block is to be coded using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 3104 includes performing, based on the determining, a conversion between the current video block and a bitstream representation of the current video block, where the performing the conversion is based on a rule of co-application of the MIP mode and another coding technique.

In some embodiments for method 3100, the rule specifies that the MIP mode and the another coding technique are used mutually exclusively. In some embodiments for method 3100, the rule specifies that the another coding technique is high dynamic range (HDR) technique or a reshaping technique.

FIG. 32 shows an example flowchart of an example method 3200 for matrix-based intra prediction. Operation 3202 includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode, where the performing the conversion using the MIP mode includes generating a prediction block by applying matrix multiplication using matrices of samples obtained from a row and column wise averaging of previously coded samples of the video, and where the matrices depend on a bit-depth of a sample.

FIG. 33 shows an example flowchart of an example method 3300 for matrix-based intra prediction. Operation 3302 includes generating, for a current video block of a video, an intermediate prediction signal using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 3304 includes generating, based on the intermediate prediction signal, a final prediction signal. Operation 3306 includes performing, based on the final prediction signal, a conversion between the current video block and a bitstream representation of the current video block.

In some embodiments for method 3300, the generating the final prediction signal is performed by applying a Position Dependent Intra Prediction Combination (PDPC) to the intermediate prediction signal. In some embodiments for method 3300, the generating the final prediction signal is performed by generating the previously coded samples of the video with the MIP mode and by filtering the previously coded samples with neighboring samples of the current video block.

FIG. 34 shows an example flowchart of an example method 3400 for matrix-based intra prediction. Operation 3402 includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode, where the performing the conversion includes using an interpolation filter in an upsampling process for the MIP mode, where, in the MIP mode, a matrix multiplication is applied to a first set of samples obtained from a row and column wise averaging of previously coded samples of the video, and the interpolation filter is applied to a second set of samples obtained from the matrix multiplication, and where interpolation filter excludes a bilinear interpolation filter.

In some embodiments for method 3400, the interpolation filter includes a 4-tap interpolation filter. In some embodiments for method 3400, a motion compensation for chroma components of the current video block is performed using the 4-tap interpolation filter. In some embodiments for method 3400, an angular intra-prediction of the current video block is performed using the 4-tap interpolation filter. In some embodiments for method 3400, the interpolation filter includes an 8-tap interpolation filter, and a motion compensation for luma component of the current video block is performed using the 8-tap interpolation filter.

FIG. 35 shows an example flowchart of an example method 3500 for matrix-based intra prediction. Operation 3502 includes performing a conversion between a current video block of a video and a bitstream representation of the current video block according to a rule, where the rule specifies a relationship between applicability of a matrix based intra prediction (MIP) mode or a transform mode during the conversion, where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, and where the transform mode specifies use of a transform operation for the determining the prediction block for the current video block.

In some embodiments for method 3500, the transform mode includes a Reduced Secondary Transform (RST), a secondary transform, a rotation transforms or a Non-Separable Secondary Transform (NSST). In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not to be applied in response to the MIP mode being applied to the current video block. In some embodiments for method 3500, the rule indicates whether to apply the transform operation using the transform mode based on a height (H) or a width (W) of the current video block. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W≥T1 and H≥T2. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W≤T1 and H≤T2. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W≥T1 or H≥T2. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W≤T1 or H≤T2. In some embodiments for method 3500, where T1=32 and T2=32. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W+H≥T. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W+H≤T. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W×H≥T. In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is not applied to the current video block in response to W×H≤T. In some embodiments for method 3500, T=256.

In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is to be applied in response to the current video block being coded with MIP mode. In some embodiments for method 3500, a selection of a transform matrix or kernel for the transform operation is based on the current video block being coded with the MIP mode. In some embodiments, the method 3500 further includes converting the MIP mode to an intra prediction mode; and selecting a transform matrix or kernel based on the converted intra prediction mode. In some embodiments, the method 3500 further includes converting the MIP mode to an intra prediction mode; and selecting a transform matrix or kernel based on a classification of the converted intra prediction mode. In some embodiments for method 3500, the converted intra prediction mode includes a planar mode.

In some embodiments for method 3500, the rule indicates that the transform operation using the transform mode is applied to the current video block when the MIP mode is disallowed from being applied to the current video block. In some embodiments for method 3500, the rule indicates that a Discrete Cosine Transform Type II (DCT-II) transform coding technique is applied to the current video block coded using the MIP mode. In some embodiments for method 3500, the bitstream representation of the current video block excludes signaling of transform matrix indexes for the DCT-II transform coding technique. In some embodiments for method 3500, the performing the conversion includes deriving a transform matrix to be used by the DCT-II transform coding technique. In some embodiments for method 3500, the bitstream representation includes information related to the MIP mode that is signaled after an indication of a transform matrix.

In some embodiments for method 3500, the bitstream representation includes an indication of the MIP mode for the transform matrix. In some embodiments for method 3500, the rule indicates that the bitstream representation excludes an indication of the MIP mode for pre-defined transform matrices. In some embodiments for method 3500, the rule indicates that the transform operation using a transform skip technique is applied to the current video block in response to the current video block being coded with the MIP mode. In some embodiments for method 3500, the bitstream representation of the current video block excludes signaling of the transform skip technique when the current video block is coded with the MIP mode. In some embodiments for method 3500, the rule indicates that, for the current video block coded with the MIP mode, the MIP mode is converted to a pre-defined intra prediction mode when the transform operation is performed by selecting a mode dependent transform matrix or kernel. In some embodiments for method 3500, the rule indicates that the transform operation using a transform skip technique is disallowed for the current video block that is coded with the MIP mode. In some embodiments for method 3500, the bitstream representation excludes a signaling that indicates a usage of the transform skip technique. In some embodiments for method 3500, the rule indicates that the transform operation using a transform skip technique is allowed for the current video block that is not coded with the MIP mode. In some embodiments for method 3500, the bitstream representation excludes a signaling that indicates using the MIP mode.

FIG. 36 shows an example flowchart of an example method 3600 for matrix-based intra prediction. Operation 3602 includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where the performing the conversion includes deriving, according to a rule, boundary samples by applying a left bit shift operation or a right bit shift operation on a sum of at least one reference boundary sample, and where the rule determines whether to apply the left bit shift operation or the right bit shift operation.

In some embodiments for method 3600, the rule defines that the right bit shift operation is applied in response to a number of shifted bits being greater than or equal to zero. In some embodiments for method 3600, the rule defines that the right bit shift operation is applied using a first technique in response to the number of shifted bits being greater than zero, and where the rule defines that the right bit shift operation is applied using a second technique in response to the number of shifted bits being equal to zero, where the first technique is different from the second technique.

In some embodiments for method 3600, the boundary samples upsBdryX[x] are calculated using one of following equations: upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i]+(1<<(Log2(uDwn)−1)))>>Log2(uDwn), if uDwn>1, or upsBdryX[x]=refX[x] if uDwn=1, where uDwn is equal to a function of the current video block size and a boundary size, where refX [x] indicates a number of reference samples x, where >> indicates the right bit shift operation, and where << indicates the left bit shift operation. In some embodiments for method 3600, the boundary samples upsBdryX[x] are calculated using following equation: upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i]+(1<<Log2(uDwn)>>1))>>Log2(uDwn), where uDwn is equal to a function of the current video block and a boundary size, where refX [x] indicates a number of reference samples x, where >> indicates the right bit shift operation, and where << indicates the left bit shift operation.

In some embodiments for method 3600, the boundary size is predefined based on the current video block size. In some embodiments for method 3600, uDwn is calculated as uDwn=nTbs/boundarySize, wherein nTbs and boundarySize represent the current video block size and the boundary size, respectively. In some embodiments for method 3600, the boundary samples upsBdryX[x] are calculated using one of following equations: upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i]+(1<<(Log2(uDwn)−1)))>>Log2(uDwn), if nTbs>boundarySize, or upsBdryX[x]=refX[x] if nTbs=boundarySize.

FIG. 37 shows an example flowchart of an example method 3700 for matrix-based intra prediction. Operation 3702 includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where the prediction samples predSamples[xHor+dX][yHor] are determined according to following formula in the upsampling operation: predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor, and predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer, where offsetHor and offsetVer are integers, where upHor is a function of the current video block width and a pre-defined value based on the current video block size, where upVer is a function of the current video block height and the pre-defined value based on the current video block size; where dX is 1 . . . upHor−1, where dY is 1 . . . upVer−1, and where xHor are positions based on the upHor and yHor are positions based on the upVer. In some embodiments for method 3700, offsetHor=upHor/2, and offsetVer=upVer/2.

FIG. 38 shows an example flowchart of an example method 3800 for matrix-based intra prediction. Operation 3802 includes generating, for a conversion between a current video block of a video and a bitstream representation of the current video block, an intra prediction mode for the current video block coded with a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation. Operation 3804 includes determining a rule for storing information indicative of the intra prediction mode based on whether the current video block is coded with the MIP mode. Operation 3806 includes performing the conversion according to the rule, where the rule defines that the bitstream representation excludes a storage of information indicative of the MIP mode associated with the current video block.

This patent document may refer to bitstream representation to mean coded representation and vice versa. From the foregoing, it will be appreciated that specific embodiments of the presently disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the presently disclosed technology is not limited except as by the appended claims.

Implementations of the subject matter and the functional operations described in this patent document can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing unit” or “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

It is intended that the specification, together with the drawings, be considered exemplary only, where exemplary means an example. As used herein, the use of “or” is intended to include “and/or”, unless the context clearly indicates otherwise.

While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document. 

What is claimed is:
 1. A method for video processing, comprising: determining, for a conversion between a chroma block of a video and a bitstream of the video, whether to apply a first prediction mode on the chroma block; generating prediction samples for the chroma block based on the determining; and performing the conversion between the chroma block and the bitstream; wherein in responding to determining to apply the first prediction mode on the chroma block, the prediction samples are generated by performing a boundary down-sampling operation based on a size of the chroma block, followed by a matrix vector multiplication operation, and selectively followed by an up-sampling operation.
 2. The method of claim 1, wherein in responding to determining not to apply the first prediction mode on the chroma block, the prediction samples are generated by performing a luma intra prediction mode conversion operation, followed by a chroma intra prediction mode derivation operation, and followed by a general intra samples derivation operation.
 3. The method of claim 1, wherein determining to apply the first chroma prediction mode on the chroma block is based on a first luma prediction mode of a first corresponding luma block being same as the first chroma prediction mode.
 4. The method of claim 3, wherein determining to apply the first chroma prediction mode on the chroma block is further based on a value of a syntax element intra_chroma_pred_mode, and wherein the syntax element intra_chroma_pred_mode is used to specify a mapping relation between a chroma component intra mode and a luma component intra mode.
 5. The method of claim 4, wherein the syntax element intra_chroma_pred_mode specifies that a DM mode is applied on the chroma block, and wherein in the DM mode, the chroma component intra mode is identical to the luma component intra mode.
 6. The method of claim 3, wherein the first corresponding luma block is a luma block covering a luma sample corresponding to a top-left sample of the chroma block.
 7. The method of claim 2, wherein in the luma intra prediction mode conversion operation, a converted luma prediction mode is derived based on a second luma prediction mode of a second corresponding luma block.
 8. The method of claim 7, wherein the second corresponding luma block is a luma block covering a luma sample corresponding to a center sample of the chroma block.
 9. The method of claim 7, wherein in responding to the second luma prediction mode being same as the first chroma prediction mode, the converted luma prediction mode is derived as a normal intra mode.
 10. The method of claim 9, wherein in the normal intra mode, distance-based weighted calculations are applied on reference values in vertical direction and horizontal direction to generate prediction values.
 11. The method of claim 2, wherein in the chroma intra prediction mode derivation operation, a second chroma prediction mode is derived for the chroma block based on the converted luma prediction mode, and wherein the second chroma prediction mode is different from the first chroma prediction mode.
 12. The method of claim 3, wherein in response to a size of the chroma block being same as a size of the first corresponding luma block, same matrix coefficients are used in the first chroma prediction mode and the first luma prediction mode.
 13. The method of claim 1, wherein the conversion includes encoding the chroma block into the bitstream.
 14. The method of claim 1, wherein the conversion includes decoding the chroma block from the bitstream.
 15. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, for a conversion between a chroma block of a video and a bitstream of the video, whether to apply a first prediction mode on the chroma block; generate prediction samples for the chroma block based on the determining; and perform the conversion between the chroma block and the bitstream; wherein in responding to determining to apply the first prediction mode on the chroma block, the prediction samples are generated by performing a boundary down-sampling operation based on a size of the chroma block, followed by a matrix vector multiplication operation, and selectively followed by an up-sampling operation.
 16. The apparatus of claim 15, wherein determining to apply the first chroma prediction mode on the chroma block is based on a first luma prediction mode of a first corresponding luma block being same as the first chroma prediction mode.
 17. The apparatus of claim 15, wherein determining to apply the first chroma prediction mode on the chroma block is further based on a value of a syntax element intra_chroma_pred_mode, and wherein the syntax element intra_chroma_pred_mode is used to specify a mapping relation between a chroma component intra mode and a luma component intra mode.
 18. The apparatus of claim 15, wherein the syntax element intra_chroma_pred_mode specifies that a DM mode is applied on the chroma block, and wherein in the DM mode, the chroma component intra mode is identical to the luma component intra mode.
 19. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine, for a conversion between a chroma block of a video and a bitstream of the video, whether to apply a first prediction mode on the chroma block; generate prediction samples for the chroma block based on the determining; and perform the conversion between the chroma block and the bitstream; wherein in responding to determining to apply the first prediction mode on the chroma block, the prediction samples are generated by performing a boundary down-sampling operation based on a size of the chroma block, followed by a matrix vector multiplication operation, and selectively followed by an up-sampling operation.
 20. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining whether to apply a first prediction mode on a chroma block of the video; generating prediction samples for the chroma block based on the determining; and generating the bitstream based on the prediction samples; wherein in responding to determining to apply the first prediction mode on the chroma block, the prediction samples are generated by performing a boundary down-sampling operation based on a size of the chroma block, followed by a matrix vector multiplication operation, and selectively followed by an up-sampling operation. 